Farid,
in literary language you can choose between "поезжай", "езжай" and "съезди".
Occasionaly I use (and some people around me use) "едь", but it is considered a questionable form.
"Ехай" is something my freinds (Moscow) would never say, and it sounds rural. In my city it is a form that makes most educated speakers laugh... well, mostly because it can't be heard here.