The Leopards will get there first because theyre already in Europe, and the supply chains can easily be integrated in Ukraine when compared with the American tanks. The Leopard also uses a diesel engine that the Ukrainians are more familiar with.
The M1 Abrams will have to be sent in by sea, and they will need to have their own unique supply chains because the M1 has a jet engine that needs aviation fuel instead of diesel, so we're looking at least 6 months for the Abrams to become operational. These big issues were the reasons why the US wasnt keen to send the M1, and only did it because the Germans demanded they commit first.
The British Challenger II will also need their own separate supply chain due to their main gun, so all this could be one hell of a logistics problem for the Ukrainians. But then again, I doubt theyll complain because they need it all.
Spain is gonna send 50+ Leopards? Holy cow.