I always thought the TNT2 64 had 64Mb, but I guess that doesn't make sense because my TNT2 ultra has 32Mb.
I guess my vote is for the TNT2, but I have no idea what the other card is like so I'm not really voting.
if you want my opinion the ati rage 128 is a 128 bit card (processor is 128 bits of band width but the tnt2 is 64 bit width so i think that the ati must be more powerful than the tnt2 at least a little bit .
Why dont you benchmark your system with both cards (one at a time) with 3dMark2000? This will give you a performance benchmark and you can also see the picture quality of each as compared to a reference image.