I bought the Waves Classic Compressors bundle yesterday and wondered if there is a noticeable difference between those and the one from UAD regarding sound and CPU usage.
Has anybody tried both and compared them?
They focus on the sound of the plug ins not really the CPU usage. I would imagine the UAD plugs would be a clear winner on CPU load since they off load most of it. Personally they all sound good enough to me (I haven't tried the UADs since I don't have the break out box). They should be smooth, slow attack, transparent compressors with a touch of tube modeling.
I know you asked specifically about waves but there are a number of others as well to consider:
I haven't directly compared those two in a shoot-out, but I can attest that most UAD plugins sound better to me than their Waves counterparts. They are possibly the highest quality plugins I've ever used. I don't touch many Waves plugs since we acquired some UAD2 cards.
CPU usage will be lower with the UAD plugins, because the UAD cards are meant to handle the grunt of the processing, at the expense of the bandwidth of whatever connection you use to get the UAD2 card hooked up to your computer. So if you use a ton of firewire hard drives, then you get a UAD2 Satellite, you'll have issues because even if you don't use many plugins, the UAD2 reserves the bandwidth that it might need (this might have changed since I last read about the satellites).
If you're interested, I found this interview with UAD's chief scientist to be pretty cool: