The Unreal Engine is very, very good and can produce some truly impressive visuals - look at UT3, Bioshock and Batman at full settings and they look fantastic.
However, in my opinion, the CryEngine wins hands down. It can produce visuals that are stunning too, but for me it's more impressive because of the way it works out the visuals in such details. If you put the settings up to Very High on everything, then stand on the beach and watch the sun filtering through the leaves on the trees and landing on the gently lapping waves, I defy anyone to come up with a more impressive graphical tour-de-force on a PC.
They both look great, but the CryEngine works much harder to produce it. That's why it's much harder on your PC, but when you find those little moments that make the difference, that's when you appreciate it.
My two cents. I know others think the Unreal Engine's better as more PCs can maximise it, but you asked for the best, not the best on an average PC.