Chamberlain or LiftMaster are the only openers I will recommend. I would recommend the LiftMaster over the Chamberlain because the LiftMaster uses a solid rail vs the Chamberlain's put together type rail. If there is a LiftMaster dealer in your area they may sell you one outright, or if that isn't an option, a Chamberlain is still fine.
As for power ratings, don't buy into them. You can easily get by with a 1/2 hp opener, it is all we sell, we put them on anything from an 8x7 all the way up to an 18x8. The thing that takes an opener out is a hard working door regardless of it's hp rating.
As for the drive type, I prefer the belt drive over anything. The only other one I will recommend is a chain drive, preferably an all chain drive. The chain drive is louder than the belt drive, that is why I like the belt drive better. I hate screw drives, too many plastic parts, they are just cheap, no matter what brand.
Hopefully this helps.
