I think the currently fastest is Hedera (HBAR), at 2 minutes per transaction or so, and that it's also the most decentralized, without that mechanism other crypto currencies have that the more you own, the stronger your power over the network. There's still some power at the nodes level though, in that if they all coordinate they can shutdown the network for whatever reason. I also read it's designed such that those metrics improve as the network grows.

But I'm not a specialist, I'm just interested in the technology and play with it a little, so take what I wrote with a grain of salt.