Indeed the french armor has it's own national designed systems, compatible with NATO standards but still with it's own specificities which are often the basis for special and inovatives weapons designs, even if lack of money means most of those are never introduced (for exemple the Leclerc was one of the first western tank designed with main gun fired guided projectiles in mind). When it first appeared the french gun was one of the best availlable and gave the Leclerc a lot of it's lethality, especially on the move. The fast reload time provided by it's automatic loader (which is, I think, still currently the best one installed in a western tank) also improved the tank's abilities.
But low production series and high technology meant quite high costs, probably too much when compared with all the second hand Abrahams and Leopard and even new build tanks from large series availlable.
Leclerc is small and performs very well in desertic settings, so it could have been a good technical choice for Australia, but politics would have prevented it. Also Leclerc have the avantage of having only 3 men onboard against 4 in any other western tank.
Leopard 2 would have been easier to get by due to larges stocks availlability and are fearsome beasts, especilly inthe latter variants, many technical analysis put it in front of the Abrahams. Outside of Merkava IV I'm not sure many tanks could be said to be better.
Challenger 2 were produced in too small quantities (about half of the amount of Leclerc built) and had too many defects to be seriously considered, also not being on NATO amunitions standards.