Sol Vista blew both of those places out of the water IMO as far as the caliber of trail design and construction. I thought Trestle was boring and keystone was average. Trestle is not that challenging and keystone just hasn't made that good of use of their space and terrain. Could be 10x better. Sol Vista is a small mountain, but you can tell the guys there really know how to ride bikes. Everything from the beginner trails to the hard stuff is awesome. At trestle you'll be pedalling to make it down the blue and green runs at a fun pace.
I rode at WP, Keystone and Copper last summer and enjoyed all 3. Being from the Northeast WP seemed more like Highland but a little more beaten up, like Highland is at the end of the season with all the braking bumps and chatter on the man made trails. Copper was fun and cheap, not a lot of trails but I really enjoyed them. Keystone is a big mountain with some long runs and some more "traditional" DH terrain that I'm used to from the Northeast. I'd have to say I enjoyed Keystone the most as it had by far the longest runs, only places I've ridden longer runs is Whistler up Garbanzo. Would have liked to try Sol Vista but didn't have time for another stop plus my son was at Woodward in Copper. Thing that impressed me most about WP was there fleet of DH rentals/demos, some of the highest end demos I've ever seen, no need to pack a bike if you're heading there.
WP's rainmaker trail descends 1000+ ft and has a TON of jumps in the 20-30' range. No Quarter, Be All and Cruel and Unusual are also fun flowy trails. Keystone has much more "real" dh that's technically challenging like High Speed Dirt, Jam Rock, Helter, Evenflow and more. Keystone's jumps are not built as well as Wp's and usually carry more potential for injury if anything goes wrong.
I think what you like depends on your skill level and terrain preference, WP is going to seem a little boring for a really good rider after a day or 2 and is devoid of decent steeps/tech. Sol Vista is the place to go if you want bigger jumps and drops but has no challenging tech, go to Keystone for tech. You really can't get all of it on one mountain, it's kinda strange...
Below is some onboard video from yesterday at Trestle, if you want a rider's view. Search & Seizure, the first trail in the video, is a fun flowy single black trail, and Bear Arms is typically used for DH race runs- it's flat and rough.