I'd go PzIII and Jagdpanther, and if you can afford it I'd get the Imex/Taigen versions of both tanks. Have you decided if you want to go airsoft or IR? You can get the Imex/Taigen tanks in either.

I started out with a $125 Heng Long jagdpanther and turned it into this

https://www.youtube.com/watch?v=ra1PPocvTcI About $700 later.