Do you prefer your tanks large or minifig scale?
For larger 1/32 ish scale:
Quan Guan makes modified Cobi tank designs
Cobi itself is really good but costs as much as Lego
Kazis Abrams tank is cheap, authentic and a must have
Xingbao also has very authentic models but are more expensive
Enlighten has a very old line of afvs with large prebuilt pieces
Sembo has a modern army series with mostly Pla afvs
For minifig scale tanks
Gudi has very cheap tanks in a lego city style
Kazi has lots of great misc afvs under the field army name but theyre hard to search nowdays due to age
Sembo and Sluban are making cool ww2 sets but >>7936830
Slubans quality isnt that good
Jie star has cute chibi afvs but theyre as expensive as lego
Enlighten/qman make military sets on the more cartoony (as in cnc generals) side
Pic related is Kazi Abrams next to Xingbao Challenger, some of the best block tanks imo.