Purely from a usage point of view.... Ive used the following

AOL - Although they get slated a lot, I used these for 3 years and was only unable to get online twice (once was my own daft fault). The thing with these is to get a router and unput the login details there so that you dont have to install the aol software.

Orange - Who I am currently with. Speeds are ok. Can occasionally have downtime however seems to be getting better all the time. Plus ya get a free voip connection with ya wireless router .. Free calls

Sky - Pain in the ass for knocking you offline. Speeds may be good but untill the service improves I wouldn`t touch them with a bargepoll