Which gamemode are you playing, 1v1 or teamgames?
For teamgames go for puma then a luchs. Soon after your puma is out HEAT rounds will unlock, and they are fantastic. They will give your puma +40 damage and penetration, which is more than enough to deal with any other vehicle on the field. Focus on vetting and make sure you use the vet1 ability to lock turrets. Once you get that off you can drive around and beat any medium tank. At vet3 you get a damage boost, and the puma will be doing the damage of a jackson with twice the fire rate, more mobility, smoke, and the turret lock ability. Very fun to use. In the laste game get a sturmtiger and wipe infantry with it. Keep your puma alive.
You can also use the armored detection to find where vehicles are like allied arty, medic trucks, or tanks and try to dive for it.
If you are talking about 1v1 it's not a very good doctrine. The abilities come fairly mid-game, and it is very rare you will fight against unsupported vehicles you can circle. The Sturmtiger is also much less effective.
Thank you ı mainly play 1v1 for ranking up but ı love teamgames too. So for 1v1 ı will change it with special operations for command panther.