Dual Core is decent for now but if quad core fits your budget then go for it for future purposes, and maybe even some of the games you play now will benefit from quad core. More and more things are becoming quad core optimized so the Phenom II is the smarter move.
Just make sure you take a look at i5 as well and see if that fits your budget.
you do realize most major vendors use parts from foxconn right? the only motherboard brand that does not is EVGA and i heard even then its 50/50. stay away from i5 period until they get this crap sorted out.