I've yet to find anything as slow and inefective as the AMX40 tbh, the T28 leads to the KV-1 so is worth it and although the T28 has paper thin armour even for a medium and is a large target, its also very nippy for it's size and carries a decent gun once upgraded.
I'm up to tier 6 on quite a few trees now and personally enjoyed the German Tank Destroyers the most, the Hetzer and the Stug are great fun to play if you can do without a turret.
The T28 is crap but it's a fleeting tank as its only something like 13k to unlock the KV1. You could even suicide scout for a couple of hours on it and get rid at the very worst.
German TD's are great. I liked them all up to the Ferdinand, whatever you do do not choose it over the Jgdpanther 2 when you get there, the 200mm armour on it is worthless as it's only the upper front plate and it's practically vertical meaning no dings unless angled. You
have to hide the lower front plate as it's huge, paper thin and your engine is right there. In hind sight i'd have taken the Jagdpanther 2 as everything will pen you on either and it has
much better maneuverability, the Ferdinand is slooow. The gun on both is awesome.
Jgdtiger i'd probably like if i liked the matches at T9 but i don't, so i don't like it.