I have 10.6 installed on both high-end and low-end configs and performance is great (as appropriate for the level of GPU) across the board. While OvrClkr suggests that 10.4 are the most stable, I would recommend that you really can't go wrong with the 10.6 version. Up to you. Either version will meet most needs.
OvrClkr is correct in that "goodness" can be variable. I am using 10.6 mobility version and with IGPs (along with the standard versions) and I am quite pleased with the performance. What IGP do you have?