In the Bail Enforcement Class (Bounty Hunter) I took in Seattle - part of the course was using pepper sprays. We tried on each other:
Sabre
Fox Labs
Cold Steel
There was about 40 of us in the class and over the week we each took a full face hit from each one. (NOT fun.

)
Hands down the one we all agreed was the most painful and fastest acting was the Fox Labs.
That is what I got for my wife and daughters.
You really can't go wrong with any of them - they ALL hurt like a mother-chicken - but the Fox Labs was HOT!
5.3 million Scoville Units.

No other brand comes close.
cheers
tire iron