The rarest most expensive one!

Seriously... for availability/bang for the buck I'll continue praising the "Chinese 12k" (about 1 micron) forever, in this sea of expensive "exotic" finishers. It's tough to beat... 20-30$ and quite versatile but can be kind of slow if you don't use it with slurry.

Else, I'd consider the naniwa 12k (~8x3" / 72$) or Shapton 16k (~8x3",95$) if you prefer bigger stones.

It seems like you're only really looking to get your razors sharp and enjoy a nice shave so I wouldn't really recommend the Japanese naturals to get like... 0.000000112% more smoothness out of them...