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Personally, I've listened to several of the Sony and Sennheiser models, the Amphony, the xdream, and a few others.
I would only spend money on the xdream or the Amphony. The others had sound that was pretty unbearable IMO.
The xdream is infrared, so it has *no* RF interference, but it requires direct line of sight. The Amphony is RF so it can be used through walls, but is susceptible to RF interference. While most of the other RF models on the market use 900MHz or some other range, which is pretty common, the Amphony uses the 2.4GHz range. It has better reception than most of the other RF systems I've tried, but because of the frequency range it uses, it is susceptible to interference from 802.11b networks, 2.4GHz cordless phones, and some microwave ovens
I'm not sure I can really pick one over the other, since I didn't own them simultaneously. If you held a gun to my head, I'd probably guess that the xdream is a bit better sounding, but the Amphony was a bit more comfortable to wear