The Corbin is a completely new seat, and very comfortable, I'm with most of us who say they are the best. The Corbin has a shape all of it's own. I don't have one now, but I'm workin on it. I do have a gel seat, it's pretty good, and I think an improvement over stock. It's wider, flatter, and harder than stock. It has a gel pad on the top under the leather. The thing I dislike, is personally, I feel like I keep sliding into the tank. I'll be selling mine soon too. They tend to go for around $150 used on ebay.
The stock is pretty obvious, just covered foam. All 3 are different, just depends on which you like best