There are 5 or 6 different versions of Guinness produced for different markets. They’re not very different from one another.Supposedly the Guinness that's sold to us poor dumb Americans is a far cry from the real thing. Not sure just how true that is though.
The big thing is finding a bar that keeps their lines clean and pours it properly and at the right temperature (50-55F, cellar temperature). I used to know the local Guinness rep and he would drop in on bars here and make sure they were doing things right. It makes a real difference.