I also say that the belt drive models are the way to go. I just got two Liftmaster Elite 8550 openers earlier this month. This was an upgrade from the battery backup Craftsman's that I bought a year ago, also belt drives. Craftsman, Chamberlain and Liftmaster are all the same really, but only the Liftmaster has a solid single-piece beam, the Craftsman and Chamberlain models are sectional square tubing. While the Craftsman was much quieter than my Genie screw-drive, the Liftmaster with the solid beam is even quieter. The MyQ iphone interface is the main reason I upgraded, but the solid beam is why I paid a little extra to get the Liftmaster. But I think any of the belt drives are a good choice.
As a side note, the dealer I bought them from had this model and the 3800 Jackshaft models on display in the garage door showroom and the beltdrive was just as quiet or quieter. But if you want a vehicle lift, the jackshaft may be the ticket. Also, the Jackshaft model does not have the iphone interface, which I wanted. Hope this helps!