They need to stay away from the Arjun. It’s such a piece of junk that the Indian army would rather buy decades old Russian designs than use it.
Best tanks out there are the current Abrams and Leopards. Following that would probably be the Merkava and the Armata. The LeClerc and the T-90 are probably on par with the Challenger.
The Mitsubishi and Hyundai tanks might be worth looking at.
The Abrams has the problem that at current it’s had a ton of retrofits and it’s starting to be a bit more compromised than is good for it. The hastily tacked on Trophy APS is necessary, but it too isn’t as good as it could be because it’s not really integrated into the tank. The lack of an autoloader or semi-autoloader is also becoming an issue; there is some thought that the lack of a main gun missile is also a drawback.
At 70 tons, it is also *very* heavy and there’s a lot of places on the planet it can’t go as a result.