Contactless I know about are Gateron, Kailh, and Flaretech's optical switches, and also the Steelseries Apex Pro with the OmniPoint Hall effect, also the upcoming beamspring by the input club, though its clicky and I'm unsure how smooth it expected to be.
According to Chyrosran22 the smoothest ones (or at least from the video I've seen) are the Wooting One keyboard which has the Flaretech switches and the SteelSeries one with the hall effect switches.
I have the Celeritas II with Flaretech linears and they're good, though I don't have much to compare them to exepct stock Gat yellows (KS8).
It's hard to compare smoothness but I'll say that the Flaretech switches are nice, but they do suffer from a certain scratch feel, while the gat yellow suffer from resistance instead.
The weird thing is that even though you feel as if the Flaretech switch feels rough and not smooth, there's zero binding and it moves smoothly, if that makes sense, while the Gat Yellows don't have the rough feel, they surface feels and goes smoothly, but it has this weird plastic on plastic resistance sometimes when pressing off-center.
