I'd go AMD.
As for Dell going with Intel, I'd imagine Intel is just willing to give them a better deal. Dell is in it for the profits, if they are able to make a machine cheaper because of a deal with Intel than it would cost with AMD, they will go for Intel. Intel gaming rigs still perform well. It won't be for a couple years until the performance difference between todays AMD chips and todays Intel chips will make a difference. And by then, todays stuff will be 20 months past obsolete.
Besides that, as wel all know, the graphics card makes more of a difference than the CPU. You can have the best CPU on the market for gaming, but if you are still using a MX440 AGP4x card, your rig still sucks for gaming.