It depends on the type of fighting. If it was an offensive vehicle, I'd put a Panzer 3 Ausf J. Turret on a Panther chassis with the engine in the front. Then, with the extra room in back, put extra ammo storage and accommodations for a squad of infantry. (Notice the Murkava design
) For a Defensive/limited offense vehicle, I'd mound a Porschturm (Tiger 2 turret) KwK 36 L/56 on a Panzer IV chassis with thickened, sloped armour in the front.
Defense vehicle
Porshturm = more ammo/space/sloped armour
Kwk 36 L/56 = same gun as the Tiger 1 ( more than enough killing power )
Panzer IV chassis = most commonly produced chassis of the Germans during world war 2. the reinforced/sloped armor provides extra protection and controls the crew will already be familiar with. Also allows for a lower profile than the later Tiger series
Offense vehicle
Panther Chassis = very large/ roomy without an engine in the rear. better armor than the panzer III and with a much bigger engine.
Ausf J. turret = less space required for ammo, less space required for turret/gun. Also was very effective in offensive operations on all fronts
Combination = a WW2 version of a modern APC
** Both include a gyroscope for shooting on the move