The Rezound is deceptively thin. For some reason it feels less cumbersome than a Thunderbolt and feels good in the hand. Maybe it's the edges on the back and the fact it's not super wide. It's also got a nice chrome-like strip around the bezel. Topnotch build quality overall. Camera is fantastic and the screen is incredibly sharp. If you've been spoiled by a Retina Display, you'll find it to be right at home.
The RAZR has an even better build and it is fast. Even with Motorola's UI, it's a snappy phone. The camera is decent and the screen is high-res enough, but leaves a little bit to be desired because of the Pentile screen. I'd say a big reason anyone would by this is for the design and speed over anything else.
I've noticed the Rezound doesn't run as smoothly as the RAZR at times, in particular when using third-party launchers. LauncherPro just flies on the RAZR. With static wallpaper and the 3D app drawer effect turned on, it's buttery smooth. Can't say the same for the Rezound. I mean it's nice enough, smooth, but it just doesn't feel as fast and with a live wallpaper? Forget it, the Rezound is stutter central, while the RAZR, while no longer buttery smooth, is much more adept at handling it all.
So which would I pick? The RAZR. It's fast, thin and hits the mark in most areas. If I adored the Sense interface or wanted the best camera, I'd stick with the Rezound. If I wanted the best of both worlds, however, I'd wait for the Galaxy Nexus. In fact, that's exactly what I'm doing.
