The Panther has been discussed a lot, with most people (apart from some players who always talk in favor of Allies anyway, no matter what unit we talk about) thinking it isn't too amazing. Especially the Ostheer one pales in comparison to the Tiger (already thanks to the also much discussed call-in mechanics), but also for example because it has terrible accuracy.
The OKW Panther has slightly better accuracy (it is still not very good, although the same is true for other dedicated tank destroyers like the Jackson), and it's tech building is more common. OKW also doesn't have an equivalent call in tank apart from the Jagdtiger which is however a lot more expensive and is usually only used to counter ISU-152s, and it doesn't have any other proper medium tank like the Panzer IV of the Ostheer available, so this explains why the OKW Panther is seen a bit more often than the Ostheer one (although a lot of players favour Pumas or for very late game King Tigers still).
The higher accuracy and the more accessible tech building made some people claim the OKW Panther is "fine". But is it really? If we take into consideration the fuel penalty for OKW (trading munition for fuel doesn't equalize this gap completely and you also lose half your munition, so you pay heavily), it would seem questionable enough to me already to have to pay the same price for a (already before underwhelming) Panther that has only slightly better accuracy (and better accuracy means here to be on par with the least accurate allied tanks). But apparently for some players this was already justification enough to claim it is "fine".
Now however I took a look at the stats and noticed that there is another difference between the OKW Panther and the Ostheer Panther that no one has talked about before, and that is the reload speed. The OKW Panther has not the same reload speed as the Ostheer Panther. While the average of the actual reload speed stat is the same, there seems to be also an additional "wind down" time involved, that according to
this spreadsheet (see AC/AD column) is effectively increasing the reload time by another second every shot. This means that it has even lower DPS than the already rather low on DPS Ostheer Panther and has the lowest firing rate of any tank apart from the Elefant, Jagdtiger, KV-2 and ISU-152 (who all have higher weapon damage in return). Even tanks like the Bulldozer Sherman shoot faster!
The OKW Panther always felt like needing ages to shoot, but I just thought I was imagining things, but this indicates that it is actually true.
If you ask me, that makes the OKW Panther actually even worse than the Ostheer Panther besides the fuel Penalty for OKW. The only significant redeeming factor that remains for me are the veterancy 4+5 levels, but that is not enough justification for me for this performance, as this is really not something you can count on achieving in a game against equally skilled players.