The ST-A3 is the GOAT because of its autoloader, Type 61 just have better mobility minus the autoloader. Be aware that all of these tanks have a painful stock grind until you unlock either the M82 shell or HEATFS rounds. While the ST-A1 and A2 have sluggish gun handling and poor mobility at first, they become quite good once spaded. They are essentially glass cannons with great scopes, so you should focus on flanking and finding good sniping positions.
The STA line maybe a little rough but once you get to 8.3 and get the STB/ Type 74 C then it get much better
Prioritize ST-A3 and Type 61, only then fill out your lineup with other tanks.
The stock solid shot actually isn’t bad at all, but you still want to get M82 and M431 shells as soon as possible. I recommend having the HEAT-FS M431 as your main shell since there’s a lot of tanks you’ll meet that the M82 requires you to aim a little too much to disable and kill.
You also get a rangefinder modification, so after getting it you should be at long range as much as possible to make use of it and not get hit much. The armor is quite bad, but the turret can save you sometimes.
I still keep M82 on both my type 61 and ST-A3 since its a very solid round, now i do keep a few rounds of HEATFS(Use in case of Tiger fromt plate) rounds but i personally prefer M82 but maybe its because i just flank a lot and having a shell which if i pen tends to one shot is more preferable to having to do multiple shots or be more picky with my shots for hitting ammo. Still very fun set of vehicles
Maybe it just me but i one shotted ppls most of the time with the HEATFS and if not kill their commander/gunner then kill them right after, still bring some M82 for those time where i can shoot enemy cupola tho.