I am in my third season with the Dolphin and am totally happy with it. It cleans the pool in about four hours and basically just works. There has been a little wear on the rollers, but nothing serious yet. I have yet to need to replace anything. The bag is not as easy to clean as the one on the Diamond/Pearl, but it doesn't bother me much. I have the remote control and an glad that I got it. The remote lets me steer for the dirt and I can do a quick touch up in half an hour that way, including getting it out, cleaning the pool, cleaning the bag, and putting it away. But mostly I just set it on it's way and four hours later the pool is clean.
I have heard some horror stories about warranty repair, but then that is true of the other brands as well.