There seems to be a real movement with Obama, people are lining up outside of the auditoriums to hear his speeches.. His acceptance speeches on the internet have an incredible number (millions of) views which means listening to the whole 9min speech to be counted. There are even comparisons to the excitement the Kennedys generated. I think the Democratic party should go with it. Hilary would probably make a good president as well, but I wouldnt really see her as a 'change' candidate. Ralph Nader wrote an article recently, that during the Clinton years there were plenty of missed opportunities to get things done.
I dont believe the Republicans have a chance on this one. With such a low approval rating - fiscal mess, constitutional violations, fear politics, renditions, etc.. On the other hand if Muqtada AlSadr and his Mahdi army start a Tet offensive in Aug/Sept who knows what might happen...