Someone (a many a few others) have made it clear we don't know what 60-70 plus the new battle system has in store; so you should reserve making that decision IFFF YOUR DECISION IS BASED ON PLAY-STYLE AND COMPOSITIONS.

If however other aspects of the tanks influences your sway then there are a ton of ideas you can settle in your mind now. For certain SE will not COMPLETELY change the Lore/play style behind each tank.

Warrior will be berserker savage
Dark Knight will be mysteriously magical
Paladin will be Holy white knight

There play styles will most definitely stick close to their lore.