I think it depends on how you would implement it on ETH 2.0 or BSC. I mean the transaction fees there are still pretty high if you would want to play with lower amounts, so you probably would need some kind of deposit feature.

But aside from that I think Polygon is a good choice. I think it's easy to use and the tx fees are low (enough).

Not sure about DOT, ADA and Solana, as I have never used them for one reason or another. (Mainly because there aren't even smart contracts available right now :P)