There are very few TV series that can keep you watching beyond the first couple of series. Even less than can cope with changing their leading actor. As a kid I was too scared to watch Dr Who and would actually hide behind the sofa to catch a glimpse of the action. It's hard to believe when you watch those episodes now, and especially when I consider what my boys watch at a much younger age. Maybe I'm just a wuss.
1. Tom Baker (Fourth Doctor) 1974-1981
2. David Tennant (Tenth Doctor) 2005-present
3. Jon Pertwee (Third Doctor) 1970-1974
4. Patrick Troughton (Second Doctor) 1966-1969
5. Christopher Ecclestone (Ninth Doctor) 2005
Tom Baker WAS Dr Who. He stayed in the part longer than any other actor and really made the part his own. It wasn't hard to believe that he didn't come from this planet. The Baker years were the ones I first watched from behind the sofa. When I did eventually pluck up the courage to watch regularly I was never quite sure I really liked him. He was just a bit too odd for me to feel entirely comfortable. However, companion Sarah Jane was one of my first hearthrobs (now back on TV and still looking great in the Sarah Jane Adventures) and K9 helped make everything more humorous.
The recent revamp of the show was an unexpected success and is improving all the time. Ecclestone represented a huge change in persona and made the part much grittier. I felt he was a little let down by the story lines and it was a shame he didn't make one more series. Tennant has been a revelation. He's brought the humour back in without making the show look stupid. An actor born to play Dr. Who.
Having only seen Jon Pertwee after the Tom Baker years, I struggled with watching Worzel Gummidge as the Doctor. Subsequent viewings have made me realise how good he was and I suspect had I been born a few years earlier he'd be my number one. The Patrick Troughton era was one I discovered as the show spiralled into it's worst period (I'm talking Colin Baker and Sylvester McCoy here) and has remained a favourite ever since. An honoury mention for Peter Davidson who, history reveals wasn't as bad as first thought. He probably had the toughest gig of any Doctor having to follow Tom B but grew into the part and until the recent revamp would have claimed his place in the Top 5.