Got the Panther Ausf. D. Why should I tech to the Ausf. A? I know the cupola is different and that the Ausf. G has 10mm side armor more and no shot trap. But what advantage does the Ausf. A have?
It doesn´t seem worth the grind time.
The ausf. A has practically no reverse gear (it litterally goes like 5 km/h backwards), but both the A and G versions do get acess to APCR shells. I think the Panther G is a bit more mobile and has a better engine, but note that the side armor isn't better - it does have more mm of armor but it's less sloped. It doesn't have the shot trap, but as far as I know gun mantlets don't work yet anyway.
I played the Panther G in closed beta, there was no noticable difference in performance (compared to D) except the addition of APCR shells. However, the Panther G gets much higher matchmaking and gets pitched against IS-2s who can hardly be killed by 75mm, while their 122mm instakills your Panther where ever they hit.
So to answer your question, in my opinion there is no reason to go beyond the ausf. D. It's a great tank for its tier. Even the F doesn't seem to be worth it since it only gets a slightly better turret but once again it also has much higher matchmaking. Only the Panther II's 88mm seems like an upgrade.