Heller kits are not bad, maybe a bit overly complicated.. Their armor catalogue is still very thin, but they have interesting subjects. Their Leclerc is a pre-production item, so there would be some work to do in order to get a production model.
Revell-Germany kits are much superior in quality, and I can only recommend those, but most of their stuff is modern German vehicles.
Italeri can be very good, or sometimes not as good, depending on the origin of the molds as some Zvezda kits are marketed under Italeri's label and those are sometimes good, sometimes bad... (it's mostly the fit of the parts that is the problem, rather than the details).
There are lots of other decent model manufacturers from Eastern Europe and the old Soviet Union, such as Allan, Skif.