There have been about 30 seasons since it started in 1963 so the Doctors are averaging about 3 seasons each (although eight had just one TV movie (or several years of books and audio plays) and four did it for seven years).
big help it is. still that is alot of watching to catch up on. I only saw season 1 when The Doc met rose (when it started airing on sci fi) and a little bit of season 2 and 3 after that. then I lost my cable TT.TT.