which version of unity should i download for low end mobile and pc

Hello all
im new to unity coming from cocos2d-x
i was browsing the forum and saw allot of Complains about the newer versions (5+ )
of unity when it comes to low end mobiles .
i want to make simple casual 3d games for mobile and pc . very important to me
that the games will run also on iPhone 4s and galaxy 2 and such .
which version of unity should i download ?
p.s
i know it also depend on what i do in the game and how i program it .
but still i want to know about the UNITY side .
Thanks!

 

I'd go with the latest. For the pricing model alone you want to be 5.X series.