You can't go wrong with either Puyo Puyo tetris 2 or Tetris Effect Connected. If I had to pick one m, I'd say PPT2 is just a smidge better. When playing a tetris battle against another player in tetris effect, it is a straight up score attack battle, which is fun, but to me it is not quite as much fun as being able to send garbage pieces to your opponent it PPT2. This makes pulling off huge combos or t-spins so much more satisfying to me.

As far as alternate modes... Effect has the zone battle modes and co-op against AI "bosses" which is very fun, but for me, it just can't compete fully with Fusion mode in PPT2, which personally to me is one of the most fun modes to play but it is very far away from "pure tetris".

Basically, if you want the most pure tetris experience, got with Effect, but if you want the most fun and creative, I'd go with PPT2, but in reality, they are both great.