I vote for Unit 13 just because Rayman is guaranteed to drop in price really soon. The portable version is more expensive than the console versions, and it is an Ubisoft game which means it WILL drop in price quickly. Rayman is a fantastic game, the best platformer ever made IMO. Even so, if I was making the same decision, I would wait for Rayman.
I am actually having the same problem. I have Rayman Origins but haven't opened it yet because I am considering MLB 12: The Show and Unit 13. I think what I am going to do (after doing alot of research) is keep Rayman Origins, buy MLB 12: The Show for PS3 (I heard its better on PS3 than Vita but not sure if you have a PS3), and then wait until a patch comes out for Unit 13 to get it. I hear there are lots of glitches and the AI is terrible but its still fun, so hopefully a patch will come in a few weeks and make it really good - then I buy it at a cheaper price too cause I have a feeling Unit 13 price will drop fairly quickly.