My favorite games are MLB 12: The Show and Touch My Katmari! I played the Rayman Origins demo and it looked so amazing I had to order that as well.
As for what game you should get, it depends on your preference. Do you like sports, shooting, adventure, puzzles, etc?
From your avatar I can assume the free Motorstorm RC download would suit you nicely.
Just got a ps vita and needing to know what games to get. So help me out and tell me what's your favorite game on the ps vita?
I bought Uncharted: Golden Abyss, Virtua Tennis 4, and Ultimate Marvel vs. Capcom 3 and I by far my favorie of the three would be Uncharted. Although the story is kind of a let down, the gameplay and the graphics, coupled with an awesome score and voice acting, were what really got me going. VT4 on the Vita and on the PS3 are practically the same, save for the addition of VR (Virtual Reality (?) ) on the Vita and the Playstation Move functionality on the PS3 version. Same goes for UMVC3.