I spent quite a lot of time in both. I take the Ride 115 out if I want to stand up and fish but I take the Tarpon 120 if I don't care to stand up that day. Because the Tarpon 120 is noticeably faster, I take it when I know I'm gonna have a longer paddle or if I'm paddling back upstream to a takeout point.
- seat moves forward and back, gives you more room
- wide cockpit is comfortable
- stand up friendly
- very stable
- very high weight capacity
- lighter and much more carry friendly
- noticeably faster/accelerates quicker
- tracks noticeably better
- its still very stable, but not really for standing up
Regarding the stability of both, I'll say that I haven't met many people who aren't able to stand up in the Ride. Usually people who say they can't just don't realize that the Ride is more stable than it initially feels. The Ride's combination of a slightly rounded hull and a tri-hull design means it will roll just a little until the bulky sides of the kayak are contacting water; at that point, the kayak is rock solid.
The Tarpon is also very stable, as long as your sitting. I have never flipped it, or even felt close to flipping it while sitting. I can technically stand up and paddle, but I'm not really comfortable standing up and fishing in the Tarpon 120.