These two cards benchmarked close to each other so the reason for one over the other is for the fanboy, fangirl, fanperson will choose the ATI or Nvidia "name" and feel good.
Best of luck,
I recently picked up an Alienware fixer-upper, a blue Area-51M 766, with a 60gb Seagate HD and a 3ghz P4 CPU. The lappy is in outwardly good shape, so I thought it worth a try to return to some degree of operability.
The big question with the machine, easily the most potentially costly, is the videocard. The PDF manual I found on-line indicates that either the Geforce Go5600 or ATI Mobility Radeon 9600 is suitable. I've seen MR9600's offered on eBay as Dell Inspiron pulls (tested, they say). Whether these units are reliable is beside the point - are these MR9600's interchangeable with those used on the 766? Is there some physical or BIOS feature on cards made for the 766 that prevents me from using any other otherwise identical cards?