Recently photobucket has been increasing the filesize of uploaded images, resulting in several sig removals on sites with strict filesize limits. For that reason, imageshack is better.

Before photobucket's recent, and in my opinion completely unnecessary overhaul, I would've chosen that.

Anyway, I use ripway since they support .php files, meaning I can host my rotator there. The only downside with ripway is the 25MB per 24 hour bandwidth limit.