Other than the fact that SU85 is insane, Stug isn't that bad. They are good emergency counter to T34 and T70 if you can't hold out the extra minute for PIV, and late game multiple stugs are a great counter to IS2/ISU (if no SU85s are on the field).
One minute wait for panzer iv is always worth it. the stug should be cheaper on fuel, or SOME kind of improvement to justify its existence. what did they do to the unit since the closed beta?? I remember the stug being a great little tank back then.