I think that you mean AMD Radeon, ATI isn't anymore since the HD6000 series.
Any advice for a graphics card can only be made when you tell us what you want to do with it. If you are into gaming you should definitely got for the AMD card, which is much faster. If you just want to do "normal" stuff, like watching videos, surfing the net or doing office work, then the Nvidia is more than sufficient.
EDIT: Noticed the m in HD 6750m to late, that is a mobile graphics chip, I doubt that you will get that on a discrete card.
Last edited by TobiSGD; 12-04-2011 at 02:55 PM.