if we assume the tank that already has a finished model is the premium tank, then imo the tech tree tank looks better (at least on paper):
Side by Side Comparison:
Premium CS-52:
Techtree CS-53:
Edit: CS-52 got some buffs to the Reload Time:
Source: https://www.reddit.com/r/WorldofTanks/comments/hax3sx/so_the_polish_tier_8_techtree_medium_will_be/