I think that any premium self-defense ammo from a major manufacturer (i.e. Federal, Remington, Winchester, Speer, etc. - and note that I said "premium", not cheap practice stuff) is likely to be reasonably effective, given the time and money they put into developing it. As long as it's in line with the bullet weight and velocity of their competitors, I'll feel reasonably comfortable with it. The only exceptions to this are things like Federal's Personal Defence line, which is deliberately downloaded in terms of velocity to make the recoil more acceptable. It succeeds in this aim, but only at the expense of compromising terminal performance. Thus, I check out the specs against the competitors' offerings in that caliber. If they're roughly comparable, I'm comfortable with it. If they're too much out of line with the rest, I avoid it.
I agree with sm that accuracy and shot placement are more important than the actual round. Sure, I won't carry FMJ or ball ammo from choice, due to the risk of overpenetration: but even this will perform adequately if placed in the right spot to immobilize an attacker.
My main concern is the reliability of the chosen load in the defensive weapon(s) and magazine(s). I follow the "200-round test" religiously. That defensive ammo, in that gun, with those magazines, must feed and fire 200 rounds without a single stoppage or problem of any kind. Any difficulty, and the 200-round test begins again from Round 1. If the gun can't pass that test, I try a different brand of ammo. If the gun fails that test with two different brands of ammo, I dispose of the gun.
This can get expensive, given the cost of premium defensive ammo: but my life is worth more to me than a few boxes of ammo, and I won't compromise on this one. I'll also do the test over again for a second gun, even if it's identical to the first. Just because one gun functions fine with that ammo doesn't mean that its littermate won't have any problems. (Of course, with a revolver, one doesn't have to bother about feeding, just function. However, I still will put at least 50 rounds of my chosen defensive load through a revolver, partly to zero the sights to that load, if applicable, and partly to ensure that there are no hard primers that fail to detonate when struck. Some primers have been known to cause problems, and I'd rather find this out during testing than in a lethal-force encounter.)
