It's always personal preference, and also what game you are playing. For me, 30 is fine for anything other than a first person game, where I prefer 40 fps+. Something else to consider is what frame-rate you are used to. For example I had a pretty low end PC, and ran my games at 30ish fps and didn't complain about any lag, but once I got my new much faster PC and was playing at 60, I noticed that when I went back to 30 fps I could feel a little choppiness which I didn't pick up when I had my old PC, when 30 was normal for me.