I finished the classic series a month or two ago, and am currently listening to Big Finish audios, mostly of the eighth doctor (mainly to fill the gaps in between Seven and Nine). Not that the audio drama format is my favorite though. Pity there aren't any animated or narrated versions of the audio dramas.
As for which doctor is the best, I'm not sure I think like that. I see each doctor as a fragment of the same person, and it's hard to compare one doctor to the other. If I wanted to make comparisons, it would be more toward the eras rather than the doctors themselves.
The First doctor era, and to a lesser extent the Second, had enjoyable moments, but for the most part were very slow.
The pace that the Third doctor era has would be carried over for most of the rest of the show. While I liked many of the Pertwee serials, I wasn't a big fan of the big usage of the Obstructive Buracrat trope, and find Season 7 as a whole overrated because of it.
I look at the Fourth doctor era, like many, as 3 different eras: Gothic Horror, Comedy, and Hard Sci-Fi. Each period had strengths and weaknesses. When I first saw Tom Baker's performance in "Robot", I wasn't sure whether I would like the fourth doctor or not. It took me a few more serials before I felt comfortable with his doctor, similar to how I saw Hartnell and Colin Baker for the first time. Of Tom Baker's seven seasons, I think Season 16 is the weakest, but at least it had "City of Death".
The fifth doctor era is probably the last where consistently good stories were written, though it had it's own problems. "Warriors of the Deep" probably foreshadowed how bad stories would get in the next few seasons.
I wasn't sure I'd be comfortable with the sixth doctor after That Moment in "The Twin Dillema". As bad as that serial was as an introduction to Colin Bakers incarnation as well as bad as a whole, it still had a couple decent moments. The worst sixth doctor serial, possibly the worst doctor who serial as a whole, is "Timelash", which made my eyes bleed a minute or two of watching. Season 22 did produce some enjoyable serials, like "Vengence on Varos", "The Two Doctors", and "Attack of the Cybermen". "Mark of the Rani" was bad, but Whoflix made it a little easier to swallow. I wasn't the biggest fan of "Revelation of the Daleks", though to be fair it's the most competent Davros has ever been since Genesis. Season 23 is one which I saw entirely in Whoflix form. Of the Whoflix Trial serials, I enjoyed Mind Warp.
I really wasn't a fan of how Season 24 did things. "Time and the Rani" is just garbage, probably the worst introductory serial in Doctor Who history. It was just painful to look at. "Paradise Towers" and "Delta and the Bannerman" both had interesting ideas, but were harmed by the silly presentation. "Dragonfire" is probably the best Season 24 serial, hinting at the better serials of the next two seasons. "Remembrence of the Daleks" is fun to watch, the only problem is the special effects, which seem more dated than older serials. I didn't really care for "The Happiness Patrol" and "Silver Nemesis". "Greatest show in the Galaxy" was really good though. "Battlefield" wasn't great, but it was nice to see the Brigadier make one final appearence in Classic Doctor Who. "Ghost-Light" and "Survival" were very confusing serials that made little effort to explain what's going on. Finally, "The Curse of Fenric" is a great serial, except for the ending. I'm not going to spoil it, but sometimes it makes me wonder how Ace could forgive the Doctor so easily. In case you couldn't tell, I didn't really care for Seven's era.
Eight...had his opening and his ending, and I'm not ready to watch his ending. Who though that the TV Movie would be a good introduction to Doctor Who as a whole? It confused me a little, and I saw most of the classic series beforehand.
Well, that's my opinion of the classic doctor's eras :P
