It’s really hard to pick between the StuG. III Ausf. F/8, StuG. Ausf. G early and the StuG.III Ausf. G late…But if I HAD to pick it would be the Sturmgeschütz III Ausf.G (Late) Sd.Kfz.142/1!
Another tough question to answer…
Sturmgeschütz-Abteilung 191 operating in Ukraine/Russia. They had a really groovy field-expedient armor applied to the side and front superstructure. 
Fallschirm-Sturmgeschütz Brigade 12. in the Saint-Lô battles, there are crazy stories involved as well as some cool pictures of camouflaged StuGs with dogs hanging out with the truppen.
Panzer-Regiment Hermann Göring in Italy (crazy camouflage and some neat modifications)
The Balkans had some unique units operating such as
Sturmgeschütz-Brigade 201, again different usage of Schürzen.
Just to name a few. But duder/dudette no need to ask on anon.