I usually start with a store to get an idea or 2. Line 6 seems to be a best seller.
http://www.musiciansfriend.com/navigation?q=guitar+wireless
Aside from signal purity, comments about interference jump off the page. I'm betting that will be a big factor. 2.4ghz is the same frequency range as telephones, is it not?
...so ever since then, I always hang on to the buckle.