The only Disney bosses that you can re-fight are Rinzler in The Grid, and Pete + Beagle Boys in Country of the Musketeers. Unfortunately, no Chernabog re-fight.
I personally think that Xigbar is the best one, because he was always there to give the middle finger to the player(in terms of difficulty in KH2 and, to some extent, Days) AND to the plot