Both are pitiful, but if there absolutely isn't any other choice, the 9100 would probably be the better option. You'd need to stick to 800x600 res, disable shadows+spectator, and force shaders 1.1 instead of 1.4 to get playable framerate in my opinion. This is based on my experience with my retail 128mb R8500 which is actually a faster version of the 9100.
Another way you can look at it, any other game would probably run just fine with more than enough acceptable framerate.