I’d go with a quality 30mm (measured tyre). When I say quality, I mean a high TPI cotton side-walled open tubular style tyre like the Vittoria corsa control or similar (in whatever size will mate with your rim to create that 30mm width).
Having tried 28mm, 30mm, 32mm I reckon 30mm is the sweet spot. It’ll be just as comfortable as a 35-38mm vulcanised tyre, lighter (really does feel better to accelerate), more aero (when at high speeds). Will also give you better contact with the ground than 28mm for good grip while also being more comfortable.
I think in due course, 30mm will become the standard road tyre, with 35-40mm being for gravel/cross and >40 for more specialist stuff.