I have both a 4" Redhawk, and a 4-5/8" Super Blackhawk. The Redhawk is stainless and the Super is blued.
The first thing I ever did to the Redhawk was ditch the awful Hogue grip that it came with and went to the stock wood Ruger grips that come on the longer-barreled Redhawks. This helped the ergonomics immensely.
Side by side, the Redhawk and Super Blackhawk have a few slight differences in the cylinder (other than the obvious differences in action type). The Redhawk cylinder is a tiny bit longer, probably to allow for 320-340 grain non-compressed loads. I haven't tried to fit any of the super long heavy loads into the Super Blackhawk, but they'd probably still fit just fine. The Redhawk cylinder walls look to be just slightly thicker as well. Basically, the Redhawk was built for a lifetime of punishing maximum .44 Magnum loads. The Super is built pretty tough as well, it's just slightly more svelt than the Redhawk.
The double-action trigger pull on my Redhawk is incredibly smooth and light (especially for a Ruger!). However, I prefer the ergonomics of the Super Blackhawk. I haven't shot the Super yet (just bought it), so I can't compare their shootability.
If you don't own any other single-action revolvers, the Blackhawk and Super Blackhawk lines are a great way to introduce yourself to that platform. But for all-around use, if I had to pick only 1, it would probably be the Redhawk.