Should i parent the eyes to the mesh or join them? I want to rigg and animate my character and my question is if i should parent the eyes to the body or join it, which way is better? Does parenting things work in games?
Parent the eyes to the head.  

Joining meshes is a lot more complicated. Their modifiers join up and often their cursor is lost. Also, joining eyes in games often makes them glitch.

To set parent to the eyes, first select the eyes, then the head, after that press "ctrl P" and select "to object".