As far as I know, Quickswap is the leading AMM on Polygon ecosystem. Simply put, it's Pancakeswap on Polygon. Low swap fee is one of its traits and this helps attract a lot of projects moving to Polygon. But this might be just temporary as Ethereum is trying to improve its transaction fee and will take those projects back. Yes Quickswap is potential to be in top 5 if Polygon ecosystem keeps expanding.