I train in PSA, have been for about a year now (so still a newbie), but I love it. There are quite a few higher level dogs in our club, and we just had a trial in which we had level 2 and level 3 dogs competing.
A couple of our club members do train in SchH but I really am not that familiar with it, so I can only comment on the PSA half of this discussion.
Most of what Narny quoted is fairly accurate in my experience. Except for maybe this:
Most of the bitework is "courage tests" which can be very difficult for some dogs and it is mentally taxing.
Granted there are quite of few scenerios that are more like "courage tests". But even at entry levels, those types of bites really only make up half the required bites, and much less than half in the 3s.
In a PDC (most basic certification), there are two bites. One is a surprise attack on the handler from behind, which is a very short bite once the dog spins around. The second bite is a courage test.
Very well done PDC:
I've actually seen more dogs get ran in the surprise attack type bites than the courage test. You really have to see that type of work in person to grasp the amount of pressure the decoy (and environmentals) puts on the dog.
And there is a significant difference between the PDC and the 2s or 3s, in terms of pressure.
The PSA3 national champ '11, protection phase (long vid):
--the dog does makes a mistake on the "voran" command, he is supposed to guard, he bites multiple times.
And one of the major differences is that starting in the 1s, you do your obedience routine with at least 1 decoy on the field. In the 2s, there are 3 decoys, and they're allowed to vocalize, throw things, jog around, but no "agitation". In the 3s obedience, the decoys are sometimes actively trying to get your dog to break away and bite, and you're expected to keep the dog in attention heeling the whole time.
In the 2s and 3s OB, there is food refusal and retrieves (any object).
PSA is definitely a sport dominated by Mals, especially at the higher levels and at nationals.