I was a tanker in my former life. I have been in or operated with several on the list.
With Combat experience, the M1A1 and the Challenger have the most and are excellent tanks. The Merkava is great for what the Isreali’s need it to do.
Without much real combat experience the Leopard and the LeClerc are very good tanks.
I have met several Soviet made tanks (without Soviets inside them) and they were handled poorly and did not survive very long. If the Soviets or Russians had operated them…who knows but in general they were outclassed (and this was in my M60A1).
Those tanks that have proven themselves on the battlefield and have shown both their strengths and weaknesses are tough to pick against. We really don’t know what the Leopard II and the LeClerc would do in actual combat conditions.
On another note the Europeans often add really great stuff to their tanks because they simply don’t make that many. Again the US mass produces (sort of) the M1 series and must cut corners on some of the extra niceties and cool stuff.