10mm or .45 ACP?
Easy for me. I'd carry one of my .45's.
Since .45 ACP is still in common use by LE/Gov users, there's much more selection of modern defensive hollowpoint loads offered for it by the major American ammunition companies. I dislike having my primary defensive handgun requiring the support of custom ammo companies, as it may mean availability limitations and increased cost.
However, being restricted to 7 rounds doesn't mean having to choose between either semiauto pistol caliber listed. My revolvers are still eminently practical for common defensive carry roles.
Of course, 3 of my .45's are actually designed to use original 6-rd capacity magazines in the first place ...
Sub Club #9; .40 S&W Club #1953; S&W Club #3913
Retired LE - firearms instructor/armorer