Brian wrote a review of Petzl Am'D Locking Carabiner on May 28, 2012
This is a very well made piece of equipment, irrespective of which lock type you prefer.
Our rope rescue team uses only tri-locks and ball locks. The rationale is that, unlike a screw gate biner, a closed gate on a ball-lock or tri-lock is a locked gate. Sure - we all double check our equipment, but this lock-on-closing feature adds to our margin of safety.
You can open the gate of either of these biners with one hand, which is convenient.