Best TDs would be:
Jagdpanzer IV with 7.5cm StuK 42- Replacement of the StuG III fully enclosed,low profile, good armour, think top speed was around 20MPH.
Hetzer (Jagdpanzer 38T) - again fully enclosed, low profile, and good armour speed was in the 20MPH range again.
M18 Hellcat - for reasons stated above, superb speed, good gun, low profile.
and to give the brits something decent would be the Archer but its a rear facing gun and the same as the fireflys. Only problem is i dont think it was fully enclosed.
Just my picks anyway. They wouldnt be super powerful but they would preform good and add new GVs ive wanted in for a long time.