The T-72 is the most difficult vehicle to play, imo. I would avoid it in the beginning. The fire control is more according to WWII than to even the Leopard-1.
The Challenger is... well, the FCS is very - British, with a Playstation controller as gunner's grip.
. Tough armour, though, but weaker gun/ammo than the L44 or L55. Note that eSim claims to have modelled that correctly according to the publicly available numbers - its just that people expected it to be a tougher gunner. But so far, with the debate on that going on and on, nobody was able to come up with data supporting that expectation.
The two crewable Abrams either have a 105mm, or the L44 but still no periscope for the TC. Gunner must manually confirm ammo loading, a step that is skipped in the Leos. GPS works slightly different with the optics shifting when adding lead - the Leos do not do that, instead confirm lead by a simple red light. Best uran SABOT for Abrams, third generation is rated with 850 mm RAH , versus 840 mm RAH for latest tungsten sabot for the Leo-2s. i think this summarises the major differences in the sim. Of course, the vehicles have different armour layouts as well, with small advantages for the Leopards. The tougher armoured Abrams A2SEP is not yet crewable.
Currently the only Russian MBT with thermals is the Czechs' upgraded T-72M4 - not the T80.