Who does Zoe like in Dinosaur king Max or Rex

I wouldn't go with any of them, as there has been no definite proof (AKA creator's comments) as to whom she likes. Also, she has shown proof of liking both, but since she has known all of them since pretty much infancy or childhood, she probably feels comfortable doing what she did in the Pterosaur Legends.
Also, in the first series, all her crushes were on famous stars, and didn't show any relationship with either Max or Rex. Also, there was barely any time different between Rex's departure and Rex's return, because even though Rex spent time with his family, he returned right at the time he left, so I highly doubt Zoe had any time to gain a crush on Max in Rex's leave.