This is like the third topic about this in the past couple months.
If you have no preference, you'll be fine with any set. I prefer the GH style guitar setup over Rock Band's, but that's because I've been using the same Xplorer guitar since GH2. I do feel that the Rock Band 2's wireless guitars perform better than the GH ones however; the detachable necks on the GH ones have the potential to create a lot of problems.
I personally have never used the GH:WT drums outside of the beat ass display models at Best Buy, so I can't really comment on those, but I have heard of some registration issues with them; the only problem I've ever heard of with the RB sets were broken bass pedals.
If it were me, I'd just go with the RB2 set and get GH:WT with the extra $10 if you really want the game. I ended up selling my GH:WT guitar set I got from a referral site because the game was pretty lackluster, and the guitar was really squeeky after only a couple sessions. I believe I would get random disconnects with the guitar as well.