Gamasutra just published a comparison report between software sales on the PSP and the DS in the United States. Not surprisingly, the DS is faring better — the PSP has released 396 titles with an average of 133,000 units sold per title while the DS has released 653 games with an average of 163,000 copies sold per title. In terms of the average number of games per hardware unit sold, the ratio is 4.8 on the DS and 4.2 on the PSP.

The NPD Group also provided the data on the top 5 selling games on each device. Grand Theft Auto: Liberty City Stories takes first place with 2 million copies sold. We suspect the Rockstar sandbox title sold unusually well due to a combination of the popularity of the GTA franchise and a certain little exploit. Lastly, every title on the list are comparatively ancient (the newest game is GTA: Vice City Stories, released back in the end of 06), which doesn’t bode well for the PSP. Wanna know what other games made the list? They are available for you right after the jump.