I've settled on two self-defense calibers, the 9mm and .357sig. If I had to choose only one it would be the .357sig because of its greater overall range and application. Like fred mentioned it's a disadvantage to rely on a single boutique ammo company's supply for your ammo needs.
There is a greater supply of effective 9mm self-defense ammo but where the 9mm is pushing the envelope for that caliber the standard, run-of-the-mill .357sig self-defense rounds aren't even breathing hard.
I carry my 9mm pistols more frequently than my .357sig because of their easier CCW conceal ability, not for their semi-equivalent effectiveness. If you do end up with a .357sig pistol I do think you'll appreciate the fine distinction between the two calibers while acknowledging the worth of both.