I can tell you that you shouldn't expect more than 1-2 years out of an ADCO cover before it starts to deteriorate, as it starts breaking down into a powder form on your roof. Water permeability follows, and shortly thereafter, so do rips everywhere.
If I wanted the best cover, I'd get one made by Calmark (
http://calmarkcovers.com/, but be prepared to pay a high price. When I got a quote for a 2720 a number of years ago, it was about $600. They are made out of Sunbrella. But I did get some covers for my patio umbrella from them, and they show virtually no deterioration after maybe 6-8 years of SoCal sun. Even the zippers remain flawless.
Dave