Sylvester McCoy is far from abysmal. I love his Chaplin-esque touches and the dark mystery he bought to the character. He could be unconvincing sometimes when called upon to shout but that's because it didn't fit his character as well as the brooding menace he bought to it.
I rate Patrick Troughton as being far and away the best actor to have played the part. He's the only Doctor actor I'd put up there with the best of the craft.
I just can't get into McCoy. Being a Chaplin fan (have all his movies) I can see all the nods, so you'd think that would endear him to me more than it has. But there's just something about him that doesn't gel. I don't know if it's McCoy or what. He's a fine actor.....
But that may change as I've been doing a watch through of Who...just got to the Fourth Doctor and I'm seeing him through new eyes. Much more alien feeling than 1-3 combined and much more so than I remember him.
So it's possible by the time I'm done with McCoy I'll have a better opinion of him. Or worse...we'll see.
To the wider audience though, he's easily second only to Tom Baker.
In the UK maybe, not in the states. Doctor Who here has exploded under Smith. It's bigger than it's ever been. Under Tennant, it was still relatively unknown. For us yanks that were with nuWho since the beginning, we've been aware of the shows popularity in the UK and so understood how big Tennant was.
But Who in the U.S. was still a pretty small club that was slowly growing. It's blown my mind how much you see Who exposure now. Billboards, write up in magazines, merch displays at stores like B&N or Hastings, full page ad's in comics, and so on. Smith is now probably more well known here than Baker was, strangely enough.