Walkers aren’t tanks, they’re a completely separate vehicle classification.

That said neither in this case is better than the other because in-universe there’s a reason for having both.

Repulsortanks are just more practical. There’s a reason why militaries don’t use Walkers (especially bi-pedal Walkers, which would be very unstable)

Walkers are comically unstable

AAT/MTTs were way better 'tanks' than the AT-ST. The same can't really be said about the AT-AT, however.

AT-ST's are like watching an old man with chronic arthritis rushing for a train