Just to give my 2 pence, Ive got a laptop with the NVIDIA GFORCE 7900 GTX Go and it works with maya fine as well as anything else that I use (ZBrush, photoshop, Avid, After Effects etc)

You need to weigh up what you want to use your PC for in the mainstream and go for that.

The ATI is supported for maya so there shouldent be any problems with anything that Maya can throw at it, the 7900 isnt so you might have a couple of problems (as they apper to crop up pretty much randomly with the Gforces).