RR vs Pure?! Missed that.
Really tough to call and it all depends on what kind of mood you are in. RR is much more relaxing and straight "fun". You can just pop it in and start having a blast. It's fast, beautiful, and plays great.
Pure is so very different. The game is brutally difficult at times and really demands a lot from the player. This isn't the kind of game I think you could easily play casually on a train or something. It DEMANDS your full attention. When you really get into it, though, it's very rewarding and fun. It certainly feels more satisfying than RR in that regard, as the challenge level is quite high. The insane amount of downloadable content really adds to the value as well. Unfortunately, a 1.50 PSP is a necessity if you wish to fully enjoy it. You MUST load this game with UMD Emulator and enable the higher clockspeeds. On a normal PSP, you get ~30 fps with slowdown. On a 333 MHz PSP, you get mostly 60 fps. At 60 fps, WP could be the best looking PSP game yet released. Just amazing looking.