I'm paranoid, I say both.
I'm fine with multi-coated Hoyas, which someone tested out as actually being better than the more expensive B+W UV filters. If you can only afford one, then I'd say go with the hood, since a cheap plastic hood
(not one of those screw-on rubber ones) will be more useful and just as protective as a Canon one, and a cheap UV filter will screw up your photos more than a good one.