First tried a Leslie's low-profile reel. Ehhh. Next went to Rocky's Reel, which we've now used for several years. This reel is heavy duty and works very well, but the initial setup is non-trivial. Putting the thing together took some time, as the length of the roller is adjusted/set by drilling through the metal rather than using set screws found on cheaper/flimsier models. The reel also anchors to the pool deck via screws, which means that you need to drill into the deck to set the sleeves for the anchors. Finally, the straps holding the pool cover are affixed to the reel via self-tapping screws, rather than velcro and adhesive.
But that investment in setup time was worth it for us. We have a 20x40 free-form IG pool, and I (a small woman) can get the (12 mil) cover on and off the pool by myself, without struggling, with the Rocky's. It is easier when someone helps, but it's not absolutely necessary. The reel doesn't sag, and because of the anchoring screws doesn't tip. The Rocky's people were really helpful: I sent them a fax of our pool dimensions, and they suggested which model reel to buy, and where to install it (at the widest part of the pool, not the end--something not mentioned in the Leslie's installation instructions). The only thing that I can imagine would be easier would be an automated pool cover, but that's a whole heckuva lotta money.
I hate putting on a new cover, so anything I can do to keep the cover lasting as long as possible
I've heard good things about Fehrer (sp?) reels, too.