Well I would go for the dual core, if your a hardcore gamer and replace your hardware alot, AMD would be better. However AMD does not make dual core proessors in your price range.
This is what AMD offers in it's single core for 250$
For single threaded applications like gaming, it will kick the crap out of the intel dual core's and a 3.0ghz would easily subcome to it's power.
However, in the future when we are all dual core, you would notice the intel doing alot better.