Plenty of secondary considerations go into guessing which tank you would prefer, Leo-2 or M1. For example the conditions of war you expect you need to fight in (defensive with stressed supply lines, or offensive), and the logistics capability of your army. That gas turbine of the M1 always consumes the same stellar ammount of fuel, no matter whether chasing down the street at maximum speed, or sitting still in idle, and it always shines bright as a christmas tree in thermal displays. The fuel needs of a Leo-2-basing tank force are much, much lower, since the Leo has as many PS as the Abrams, but bases on a Diesel engine (which additionally is extremely robust, and fast to replace if maintenance demands it). The modern versions of the Leo-2 feature equivalents to IVIS system for TC's SA, while the Leo-2 always has the additional TC advantage of that TC-perisope. Maximum speed for the Leo is slightly, but not much, higher than for the Abrams, while the Abrams has a slightly better acceleration, but if these minor difference really play a role in reality or not, only real tanker can tell you - but I doubt it. Ergonomics and firing procedures in the Leo-2 seem to be easier, shorter and thus: better. the Canadians using leased Leo2A6-ers in Afghanistan say they consider it to be the best tank in the world, and prefer it to the Abrams. But as I see it, all in all both tanks in their most modern incarnations pretty much compare to each other, with both vehicles being incredibly tough armoured, and mobilised. As an enemy tank, you would not like to have to deal with either a Leopard-2A6 or an modern Abrams. The main difference imo is the logistics factor, and easier maintenance, both speaking for the Leopard.
Both tanks derive from a German-US cooperation for a future tank, but that cooperation then broke apart. However, many of the design and dimension similiarities between both tanks are explained from that.
I must admit that I still failed to have learned anything about the Challenger-2. Shame on me!
