I liked early Tennant, but later on in the series it got a bit too angsty and self-pitying for my tastes, I think he picked the perfect time to leave, however, because I do believe that further Tenant episodes would have slowly dropped in quality until it got boring.
Hartnell was a unique, and under-rated Doctor to be honest, and the special effects of the time didn't do him any favours, but he was a highly cereberal Doctor, far more inclined to use his brain to solve a problem than his future incarnations (this was, however, partly because he was pretty old and couldn't do energetic stuff), and the understanding of science at the time seems a little 'quaint' by our modern standards.
My favourite was Baker, partly because I grew up with him as the Doctor, and partly because he had Douglas Adams writing some of his stories, which was a perfect combination with Baker's personality, but I do, however, have a lot of respect for later Sylvester McCoy episodes, mainly because it was the man himself who insisted the Doctor got more adult and manipulative in his manner and whilst the series ended under him, he did a lot that helped the new episodes come back aimed more at older audiences rather than as something like the 'K9' series on childrens TV.
