Keep WipEout, specially if you have WipEout HD on PS3.
It`s the definitive WipeOut experiance now, the amount of conent after the recently released packs (which are free if you already own HD) is insane. 3 full single player campaigns, a seperate on-line campaign, cross platform multiplayer with PS3, and cross platform leaderboards. It`s almost like 3 games in one.
Unit 13 I`ve only played the demo as well. Seems like a really good game if you`re gonna compete on the leaderboards, and something that would be great to play for 10-20 minutes at a time.