Now here is something I can discuss. I am, in the parlance of the local police, a #@$% magnet. In the last six months I have had to spray seven resisting subjects. I think that may be some kind of a record. The fact that I am a CIT officer (we get the mental patients, in addition to the regular crazy scumbags) may have something to do with it. Pepper spray is not infallible. I have seen it work like a shovel to the face, and I've seen it just annoy the dickens out of the guy you just zapped. Mental condition, level of intoxication, and just plain toughness are all factors. We are currently carrying a 5.5% spray in a stream (MACE brand) as general issue. This is a vast improvement over the older 3in1 spray we carried (1% OC with CS and a marker dye). The new 5.5 is noticibly hotter and has a quicker onset of heat than the old spray. The 2 people I used it on both changed their outlook on life and cooperating with the nice officer very quickly. The other can on my belt is a 10% foam which I refer to as "The Malicious Merange". It is a truly nasty substance issued to CIT and MED personell. The foam sticks to your face, melts into your eyes, and is generally unpleasent. It is running about a 80% success rate for me, but it gets used almost exclusively on violent mental patients, so I consider that pretty effective. Problems exist with the foam however. It DOES NOT WORK in the wind. Think shaving cream fight on a windy day. Also due to the foaming agent you need a bigger can that contains less actual uses. The sprayed individual can get a big handful of the stuff and sling it back at you. Also, the percentage does not make the spray hotter, only last longer. The 5.5 spray wears off in around 20 minutes. The foam burns for an hour or more. This is important since the likelyhood is very high that if you deploy agent, you will get to expeirience the fun effects yourself when you subdue the subject (or your partner has bad aim...)
Brands that I have seen used to good effect:
FOX
Sabre
MACE 5.5 or 10%
Freeze +P
Try to stay away from the water based sprays, PDs went to them for fear of setting people on fire with a taser after spraying them. The solvent based sprays (such as Fox) penetrate the skin faster and have a much quicker onset. The water sprays seem to take up to 10 seconds to really "heat up" once deployed.
As far as dogs go, the liquid stream seems to work pretty well. Aim for their eyes and muzzle. They usually go away with a confused look and drag their snout in the dirt trying to get the stuff off. On a really angry dog you may be SOL as they have a pain threshold that is downright unbelievable. Be ready to deploy alternate means should the spray fail.
Finally, I HIGHLY suggest that if you are going to carry OC for defense that you take a hit from the brand you are going to carry (under controlled conditions of course) so you will know what it will and wont do and how you will react if the wind shifts and you get caught in the backspray. A lot of the effectiveness of OC is based on the suprise factor. Knowing what is coming helps.