Interesting thing about this query is that the responses draw the same contenders that were being championed in the late 80s (LEO II, Abrams, Merkava, Challenger, etc. MBT technology has been moving slowly.
Merkava III - great tank, in its theatre of ops. Not suitable for Europe - too wide. Some of you may know the old saw about out rail guages having been determined by the width of Roman chariots. Guess what - the width of tanks is determined by those same chariots. How so? -- tank have to fit on flatcars for transport -- Europe has standard size tunnels that tloaded flatcars have to fit through. A Merkava doesn‘t. As an aside - theory also applies to transporting AFVs in Hercs - if you forget about add-on armour until after you‘ve built the hull, you have to choose between flying in without the applique, or finding a staging area! Not that anyone would make such a basic mistake.
For MBTs, it eventually leads back to the "Leo II v. M1" question. Appropriate, since the two started out as the same project until the Germans insisted on one gun and engine, and the Americans on the others.
Aside from the question of engines, the other big concern is the source of your spare parts - do you want them coming from the U.S. or Germany. Again, if considering the European theatre (arguably no less important than ever, particularly wrt MBTs), the choice is having them closer, if the factories aren‘t destroyed (Germany) or further away, but more certain (U.S.)
As has been discussed elsewhere, the first question to be asked is "do we need tanks at all?" This is a big strategy question that goes beyond our allegiance to a particular arm, our lust for the biggest and baddest toys, and our tendency to prepare for the last war.
Unfortunately, no one seems to have the necessary bits to make the call - what do we want our military to do for us, how much notice will we give our troops (and industry) to prepare, and how much money we are willing to throw at the problem.
Maybe there is some hope - it seems that the Minister is hot for the new joint fighter - maybe the army can squeeze a few bucks out to get some new toys, too. After all, the F-18s haven‘t been around anywhere near as long as LEO I.