Petzl William Screw-Lock
The William carabiners are HMS carabiners (meaning they are designed with using them with a Munter hitch in mind). For a screw-lock, this one is excellent (but then, with a name like "William", how could someone like me, named William, consider it to be anything less than excellent?). In situations where a screw-lock is appropriate, this has been my standard for several years, along with the smaller Attache. In setting up anchors, where several ropes might be attached, the William gives plenty of room.
The disadvantages of screw-locks in general are well-known - you need to watch the direction the rope is running, since the rope can rub on the sleeve and undo the lock, and you need to remember to not overtighten the sleeve, especially after the inevitable dirt gets in the threads. Overtightening can make screwlocks very difficult to open.