I'd prefer Sen. Clinton to Sen. Obama, based on their overall positions. She is very slightly more moderate than he, though both are quite liberal. However, I do think Obama would bring some measure of civility to politics, while Clinton would bring the very opposite.
However, since AZ already had its primary (from which I abstained), and since I have no plan to vote for any of the three candidates mentioned, I won't be switching my affiliation to Democrat. I will very likely switch to Independent when I get home, though, since a party that nominates Sen. McCain can no longer be my political home.