Not, who do you want, or who will you be supporting, but rather, who do you see as the likely Democratic nominee?
Kos logged in on this topic, and see's Obama as having the advantage the way the primaries are lined up.
I'd been picking Feingold for a while, shows what I know (I also said the Democrats didn't have a chance in hell of taking the Senate or defeating Lieberman in the primary.) So, I'll say Hillary right now, not because I really believe she'll be the nominee, (and I believe she really would be the worst candidate in the general election), but just to have a pick.
And, as always, feel free to guess who the Republican will be in the comments, and pick a winner.