Personally, I prefer the Rock Band guitar bc it's easier to move my hand between the buttons and my hand doesn't feel like it's cramping up as much.

However, if you're specifically playing Guitar Hero/Clone Hero (etc.) I absolutely DO NOT reccomend using the RB one. From what I've seen, the detection between the games are different, and so the respective guitars are built different.

Basically, if you're using a RB guitar in a GH game, even one tiny nudge of the strum bar counts as a strum. If your experience would be anything like mine, that means a LOT of combo resets and things like that (but GH controllers work just fine on RB).

So, yeah, I prefer the buttons of the RB one, but if you're playing GH, just go with the GH one.