I've seen references to feats being retained when you are transformed via True Polymorph. Are ability score increases (ASIs) also kept? If not, that would seem to make feats a strictly better choice if you're aiming to be True Polymorphed.
If you are talking about ASIs you've already earned then all your ability scores get replaced (regardless of ASIs):
The target's game Statistics, including mental Ability Scores, are replaced by the Statistics of the new form.
Feats also do not carry over with True Polymorph. Just a heads up.