Gold is always the best
I have used many locking carabiners, and the Petzl Attache is by far and away the best that I have used. It is the ideal size for most setups, such as for multi-pitch anchor set-ups and it is the only locker I use for belaying. The size is large enough for multiple hitches. For belaying, it stays in place and does not seem to ever cross-load.
The one draw back that I have found, is while ice climbing, the gate can easily freeze shut. If you don't send in the dead of winter, then the attache will win you over.