The armor on the Merkava is combat proven. It has seen hits from T-55s, T-62s, T-72s, RPGs, AT-3s, and numerous other weaponry. The Merkava Mk 1 and 2 proved themselves in the 82 war very well.
The armor on the Leclerc and Leopard is most likely their own home grown Chobham, basically ceramics and steel with other high strength materials. It's obviously passed tests because its in service, so it probably does work.
Ahh...the AK-47, when you absolutely, positively have to kill every last motherf*cker in the room...accept no substitute