Go with what is the cheaper. What I shoot in 9MM shoots fine in my .380. the amount I shoot warrants reloading and what I get is what I find the cheapest, sometimes 9MM FMJ, sometimes .380 FMJ Brass I look for in bulk, again what may be cheaper. Clays powder not expensive with normal load, A tad dirty, primers all run about the same.
Have near 1000 rounds of each put away and can't see any difference in practice or target.
A gun I regret ridding is a Beretta, 9MM Luger, not hard finding bulk ammo, a hell of a lot more punch, more range.