the highest TPS i knew was WAVES which they claimed can do 300k TPS, not sure if its true though. and then there's also Cardano claim, so far there isn't a real number that can prove a project can scale up to millions.
As far as I know, those are simply claims. Nothing else. To verify the number of TPS a cryptocurrency has, some tests need to be done that will prove how scalable the underlying blockchain network is. So far, XRP and Stellar are the ones with the highest TPS because of the way they're designed (centralized). You would either sacrifice decentralization over scalability, or vice versa. It's no wonder why Bitcoin is so slow and expensive. The pioneer cryptocurrency has chosen decentralization over scalability for a very good reason. Other cryptocurrencies like Bitshares, XRP, Stellar, ARK, and Lisk are extremely fast and cheap to use because they have preferred scalability over decentralization.
Waves is also fast, but I believe its claims of 300K TPS are exaggerated. None of the cryptocurrencies I've toppled with, have reached a level of a million TPS. All I've seen are claims instead of verifiable proof from most Blockchain projects in the mainstream world. As time goes by, we'll be able to see a slight improvement in the number of TPS a cryptocurrency can handle. There's always a choice for people looking to use crypto for daily payments (XRP, XLM, EOS, ...) or as a store of value (Bitcoin, Litecoin, ...).
Nonetheless, the battle will be fierce among various cryptocurrencies with the aim of achieving the highest TPS within the mainstream world. While the average person doesn't care about this, avid crypto users (like you and me) do care. It's a matter of which cryptocurrency is the most useful to the world by providing the best scalable solutions that would keep the economy flowing for years to come. Just my opinion