It's hard to recommend a specific frequency as the amount of radio interference varies according to the location. Generally, they say that UHF is better than VHF but I've been seeing RC cars, cellphones/cordless phones and UHF radios being assigned the same frequency bands as wireless mics; I've also just read that the frequency bands assigned to UHF are being reallocated to digital TV in the US - not so much a factor here but something to think about in the future. Plan on getting a frequency agile wireless system so that you can switch frequencies in the event that some have radio interference.
