Wow...it's really hard to pick. Not so much for first place, because
Sayid is my favorite character, hands down. But second place is tougher. I voted for
Desmond, but I really love
Sawyer too - it's really almost a draw between them. Desmond has one of the most interesting storylines on the show...but Sawyer is by far the character who has grown the most over the course of the show, and I like that very much.
Fourth place for me would probably be
Hurley...although, oddly (given how few episodes he's in),
Richard Alpert would give him some stiff competition. I love a mystery...and there is no greater mystery on LOST than Richard Alpert. I am absolutely fascinated by him and, partly because he is in so few episodes, I look forward to seeing him more than any other character....always hoping that we might get some new little crumb of information about Richard. Can't. Get. Enough. Richard.

I think they need to make him regular cast for the last season. Because IMO, he's one of the central keys to the entire show - tying everything and everyone together. And perhaps the ONLY character on the entire show who seems be be nearly devoid of self-interest, but is truly thinking ONLY of the Island.