I'll go ahead and add my thoughts on this, which can probably be found in other threads on here.
Find a HP from a known and trusted name brand (i.e. a round that some law enforcement agency uses, or that is extremely common and proven), that you can run 100 or so rounds of through your carry weapon without any malfunctions so yoou know it is reliable, and stick with it. Why add unknown variables into the equation when your life is on the line. IF you have round "A", and round "B", both of which meet those criteria, I'd honestly choose the less expensive one so you can buy more of it.
The only time I mix ammo is either 1. putting tracers in a belt for a full auto, or B. putting a few tracers in an M-16 mag as per the way we do things in my unit.
Also I guess you can mix in a slug as needed into a shotgun, but that isn't really mixing it up in the mag.