Don't really know about the "best" brand of pepper spray. Our issue stuff is Freeze +P. It works.
The whole problem with it in my experience is that while it certainly can be effective at slowing down or stopping a person bent on aggressive action, the distances at which these confrontations usually happen, along with other conditions, tends to...well, let's say spread the effects of the spray among others than the intended target.
I have used, or been present during the use of pepper spray, when the good guys suffered from the effects almost as much as the bad guys.
Nature of the beast. Although directed in stream, it doesn't all stay concentrated in the face of the target. It atomizes, gets in surrounding air, and anyone close by can feel the effects to some degree...burning, watery eyes, mucus flow, coughing...especially in a closed space.
Not an indictment of the product. But like most "weapons" in the defensive tool box, it has it's down side. And if you or yours carries it, you should be aware of them.