I've been trudging through the sixth and seventh Doctors' episodes while waiting for the new series, and in hindsight it seems kinda shitty that fans laid so much blame at the feet of Colin Baker and Sylvester McCoy for the cancellation of the old show. Baker's Doctor in particular was saddled with some absolutely terrible writing and two of the worst companions in the history of the franchise (one that was never even properly introduced). But the sixth Doctor himself, especially during the Trial of a Time Lord stuff, was fantastic. Despite the garish outfit, he was a rather dark incarnation; always ignoring much of what was going on around him to figure things out and stay ahead of everyone else. A lot of violence and gruesome deaths during those seasons too, which he seldom gave a fuck about. In some ways, Smith's Doctor reminds me of him.
McCoy's version of the character is the one I'm least familiar with, but the trend seems to be continuing so far. A great take on a classic character ruined by awful stories. Definitely the schemer of the lot.
My girlfriend asked to watch a few episodes a little while ago to see what I'm always going on about, so I started her from the beginning of Eccleston's run (she digs it). I'd forgotten how good he was. Maybe my favorite of the new Doctors, in fact.