PBP, both are capable SD guns. (I know you know that already.)
If he likes the M60, shoots it well, and is completely happy with it, it'll take care of business if the time ever comes.
If he likes the G26, shoots it well, and would be happy with it, go buy him one.
If funds are an issue, I'm sure you can find something in your collection that wouldn't leave too large of a gap if you sold it to fund a G26 for your partner... I would happily sell every gun I own (with the exception of my BAR and my G20SF
) to fund a gun for my wife... She has little/no interest at this point, at least your other half is into it, even if only slightly.
As for the Glock naysayers who claim they are terrible guns to start out on... It all depends on the shooter. No gun is safe. No gun is infalliable. No gun is forgiving of major mistakes. A safety-minded person is just as well off with a Glock as a 1911, Sig, S&W, and so on, regardless of skill level.
BTW: Have you properly introduced him to your G29 yet?