Ukraine

F35s would overwhelm Ukrainian logistics capacity also Ukrainians don't have many good things to say about the Abrams in practice, from what I gather mostly weight as well as lack of reactive armour package and general sturdiness of the turret. Leo2s have similar issues: A T74 weighs just over 40 tons, that's the kind of weight Ukrainian infrastructure is made for (think random bridges in the countryside and lots of mud), Leo 2A5 55t, 2A6 62t, 2A7V 66.5t, M1A2 SEPv3 66.8t.

Send F16s and Bradleys instead. Send those Abrams to Greece they have about 500 Leopard 1s Ukraine can use and already has infrastructure for. Same weight class as the T74.

EDIT: Oh, before I forget: Send any Leo1 chassis you can find anywhere. Rheinmetall is working on Frankensteining new Skyranger turrets onto old Leo1 chassis which then will essentially be Gepard 2s -- same chassis, even more capable turret. Those kinds of systems are about the only thing that can reliably take down drones in a cost-effective manner. Also send over three Patriot batteries or five or ten.