I like all but small. Small takes a little too much effort for me to play.
As far a being able to slide up and down the neck, a proper fret dressing will fix that.
I've seen a few different styles during repairs. There's the matching recessed ones like you're talking about. The. There are ones where the ones on the cover stick out and then there's just normal screws that are recessed in the control cavity. I've also seen one with a metal cover and magnets on the inside. If I remember correctly, that one was microphonic.
Deck, railing, and outdoor furniture stains work... although i don't think they're very applicable for guitars, as they have a sort of "flexible" quality to them.