I have the RB2 drum kit with the triple cymbal expansion pack and I've played on the GH drums. I prefer the RB drums, especially since the cymbals became available. The cymbals are extra for RB but I found it to be well worth it. The RB2 drums are much more durable than the RB1 drums but I really can't say how durable the GH drum are. The cymbals for RB2 however do not work with GH (pads only). I don't know if the GH cymbals work with the RB disc.
As far as the guitar, try playing both (if you haven't already). I actually prefer the RB guitar over the GH one.
Regardless which equipment you get, both games are worth having.