I'm not great with boxing analogies, so I can't really say.
The Leo is more agile and slightly faster, with a gun with better penetration (but it's not much. We're talking mm here). But, the Chally makes up for the lack of penetration with range and accuracy, and having even more armour.
Ed, Challenger 1 took out tanks at 3.2 miles/ 5.1 KM
If I was going to pick an all round best tank, I'd probably say the Centurion. It pretty much laid the foundation for what we know as the MBT (the triangle of protection, firepower and mobility), it was incredibly reliable and robust, and it can still take upgrades. They're still in service in some places - with 120mm guns and modern electronics. Not too shabby for something that was originally designed in 1944.