It’ll be easier to recommend a starting place, if we know a bit more about your other television watching habits. What other sci-fi series are you a fan of? For example, are you a fan of classic Star Trek? Have you watched other British sci-fi like Blakes 7 or Space 1999? Are you a fan of Hammer Horror films? Do you primarily watch modern television or frequently dip into the past?
Also, and this may be the biggest question… do you have BritBox? (which is the only channel streaming the classic series), HBO Max? (which is the only channel streaming the modern series), or access to all previous episodes through torrents or an enthusiastic friend’s DVD collection, or are you considering purchasing individual episodes or sets to start with?
That said, here are a couple of recommended jumping on points:
If you think you’ll be more interested in the modern series of Doctor Who, I recommend starting with Season 5. Yes this is dropping you straight in the middle of the modern era but the Steven Moffat seasons comprising the entirety of the 11th and 12th Doctors’ runs, are (in my opinion) more consistently enjoyable than the Russell T. Davies 9th and 10th Doctor eras, which are an extremely inconsistent jumble of very good episodes (many of which were written by future showrunner, Steven Moffat) and utter crap (most of which were written by Russell T. Davies.)
The Eleventh Hour, the first episode of season 5 and the 11th Doctor, also does a fairly good job of reintroducing the character fresh to new-ish viewers. Chances are, if you have an even passing familiarity with the program, you already know what the TARDIS and regeneration is, and you can pick up most of the rest along the way from here.
If you do decide to start at the beginning of Season 1 of the new series with Rose and the 9th Doctor, just know going in that modern era Who is always going to be uneven, and the first couple of seasons were especially so. Things pick up a bit in season 2, once you get David Tennant settled as the 10th Doctor (who is much more of a “classic” Doctor than Eccleston’s somewhat brusque 9th incarnation) but you’ve still got really good episodes like School Reunion and The Girl in the Fireplace, standing alongside the worst of the worst like Love and Monsters and Fear Her.
As for the two most recent seasons 11 & 12 with the 13th Doctor… just don’t. No shade thrown on Jodie Whittaker’s portrayal of a female Doctor, but current producer Chris Chibnall is responsible for 9 of the 10 worst rated Doctor Who episodes of all time, and has about as much talent when it comes to writing sci-fi as a moldy cheese sandwich. Save these seasons for when you’re so desperate for Doctor Who that it’s a choice between this or rewatching Twin Dillemma and Time and The Rani.
If you’re looking to go back and enjoy the classic series, make sure you go in with the understanding that:
A) most of the serialized stories are several hours long and move a lot slower than modern television. Generally speaking, anything over 4 episodes is usually going to contain about 4 episodes worth of plot and 2 to 3 episodes of padding. And B) The budget of the classic series was about £5 and whatever they could nick from the BBC commissary. Sets will wobble, early green screen technology (called CSO back then) will be incredibly ugly and fake looking, and monsters will look surprisingly good in one episode and like cheap rubber Halloween masks in the next, depending on how good the production staff was as creating something out of nothining.
On the plus side, while the classic series suffers on a SFX/budget level compared to modern Who, the stories themselves are usually more consistently entertaining and well scripted… at least until you get up into the 80’s with the 6th and 7th Doctors.
As for jumping on points, there are several, depending on your threshold for classic television.
In most cases, I’d recommend starting with Tom Baker’s 4th Doctor, widely regarded as one of the most enjoyable and easiest to love Doctors, with several of the classic series’ best episodes under his belt. If you’re thinking of purchasing DVD/BluRay sets, Tom’s first season (season 12) was recently rereleased on blu-ray and contains several classic episodes, including Ark in Space and Genesis of the Daleks, two of the best Doctor Who episodes… period. Additionally, if you happen to find a copy of the Key to Time DVD set (season 16), that’s another good starting place since all the stories are linked, and (mostly) all good.
As for the rest of the classic era, here’s a brief rundown of what you’ll be letting yourself in for with each Doctor:
1st Doctor (season 1-4) - One of the hardest eras to get into, unless you really love classic black and white sci-fi. Though this was where it all started and there are some definite classics every true fan should see (especially the very first episode, An Unearthly Child, and the first two Dalek stories, The Daleks and The Dalek Invasion of Earth) they hadn’t yet developed The Doctor as the brave, brilliant, and funny intergalactic savior of the entire universe several times over. He was much more of your typical 1950’s crotchety old professor, and most of the real heroics were taken care of by the younger handsome leading man companion, Ian Chesterton. His stories tended to be rather long, and shot on a sound stage the size of a broom cupboard, where they could only afford 3 or 4 sets per episode, and everything was recorded live to tape like a soap opera (flubbed lines and all), so it’s a very different animal than what you’ll become accustomed to in later seasons. Also, about half the Hartnell stories were straight up historical adventures with no aliens, monsters, or sci-fi elements other than time travel, where the Doctor and his companions show up someplace dangerous like ancient Rome, the Crusades, or the French Revolution, and then immediately get separated from one another and spend the next 4-6 episodes looking for each other so that they can leave again.
2nd Doctor (Season 4-6) - The Second Doctor, played by Patrick Troughton, is largely responsible for setting the stage for all future Doctors. And is a good jumping on point if you want to explore Doctor Who in the 1960’s. While this period of Doctor Who was still in black and white, it’s a lot more fun and active than the 1st Doctor era, especially once you get the 2nd Doctor paired up with fan favorite companions Jamie and Zoe (Victoria can be fun too, though is a bit more of a scream-at-everything load). Sadly, a lot of the 2nd Doctor era is missing from the archives, and while many stories have now been animated to match the surviving audio tracks, they can be a bit rough to watch. If you want a taste of the 2nd Doctor at his best, I recommend beginning with Tomb of the Cybermen and The Invasion (both Cybermen stories), followed by The Dominators (which is light fun and my personal favorite Troughton story), The Krotons and The War Games, (Troughton’s epic 10-part swan song, and the story that introduces us to the Time Lords and the idea of him as a run-away in a stolen TARDIS for the first time.)
3rd Doctor (Season 7-11) - In color for the very first time and responsible for shaping a lot of what would eventually go on to become the series lore (until Chibnall bunged it all out the window with his latest version of the new series) the 3rd Doctor era is a little harder to get into for a couple of reasons. They decided to maroon him on Earth and make him the scientific advisor to UNIT, so most of his stories involve protecting 70’s Earth from alien invasions or various schemes of The Master, and to save on production costs, almost all his adventures are six episodes long… with the afore mentioned four episodes worth of plot. There are still some great episodes during his era, especially Spearhead from Space, The Three Doctors, Planet of the Daleks, and The Green Death, but even these have their “get on with it!” moments.
4th Doctor (Season 12-18) - As previously mentioned, widely regarded as the “best” era of classic Who, where it was at it’s most creative and fun. There are so many good episodes in here, it’s hard to pick just a couple of highlights, but Ark in Space, Pyramids of Mars, and Seeds of Doom are all brilliant. And if you’re a Douglas Adams fan, you’ve got to check out City of Death.
There were several mini eras within Tom Baker’s run, which may appeal more or less to you depending on your interests. Season’s 12 through the first half of season 15 (the “Hinchcliffe era”) was heavily influences by Hammer Horror, and tends to be a bit darker and scarier. Season 15-17 saw Robert Holmes and Douglas Adams take over as script editors, and tend to be a bit lighter and sillier (but still good.) And his final season, which saw the show dragged kicking and screaming into the 80’s, was a return to a slightly darker more serious version of the Doctor, though at the same time, the beginning of the era where the show realized that the public’s expectations for sci-fi had been raised thanks to big budget productions like Star Wars, and they felt the need to taking more risks and stretch their meager budget to the breaking point… which didn’t always pan out.
5th Doctor (Season 19-21) - A bit of a mixed bag. As previously noted, the show was starting to stretch itself with mixed results. You’ve got great episodes like Earthshock and Frontios, back-to-back with turds like Time-Flight and The Awakening. You’ll also see the influence of American television on the show, where the companions became louder and more obnoxious (especially Tegan and Peri.)
6th Doctor (Season 21-23) - Do not start with the 6th Doctor. This was the start of the death of classic Who, where producer John Nathan-Turner made a series of increasingly bad decisions to try to keep the show “fresh” and compete with more popular American TV series of the time. There are a few okay episodes from this era like Attack of the Cybermen, Mark of the Rani, and The Two Doctors, but by and large best avoided if you’re looking for a way into the classic show.
7th Doctor (Season 24-26) - A return to mixed bag Doctor Who. The show was just starting to find it’s footing again when it got cancelled. While Sylvester McCoy does his best, a lot of this era is crap. But then you get episodes like Remembrance of the Daleks and The Curse of Fenric, which are absolutely outstanding and the true start of “modern” Who.
8th Doctor TV Movie - A great big ball of WTF. Paul McGann is great, and it looks pretty… at times, but yeah… don’t bother with this one as a casual viewer.