Whichever your frame builder can get. If you're worried, get a couple of spare through bolts now, although I suspect that it's the OLN dimension which will trip up future proofing rather than the thread pitch.
If I'm designing for bikes with a free hand, I prefer 1.0mm pitch for everything from M6 up.
Well I haven't really seen any 1.75mm dropouts to be fair. So if neither of the other two are going to go out of fashion in the next year or two, I'll just get whichever.
Thanks. 142x12 seems to be safe for now at least
Whichever your frame builder can get. If you're worried, get a couple of spare through bolts now, although I suspect that it's the OLN dimension which will trip up future proofing rather than the thread pitch.
If I'm designing for bikes with a free hand, I prefer 1.0mm pitch for everything from M6 up.