I'm not an expert, but have asked the same questions and here's what I've learned so far.
Videos like Power Hours, Maximum Intensity Strength, and most recently Muscle Endurance are endurance workouts. Like Cathe said, if you have to go to the store and pick up a jug of milk, then hold the milk through the whole checkout line, your muscle endurance comes into play.
Slow and Heavy is the ultimate muscle building series, and Pure Strength is also a muscle building series (although not as slow from what I understand). All of the S&H are about an hour apiece, and Pure Strength is more like 40 minutes. The music is Pure Strength is fantastic!! (instrumentals of 70's rock)
The new Pyramid videos use a pyramid system - you start out with low weights on a certain exercise (say, for the quads or glutes), then do fewer reps with a heavier weight, then fewer reps still with the heaviest weight - then you do a few more reps with the medium weight again, then more reps with the light weight.
I don't know why this is different from normal weight workouts though. I have been told that if you're a beginner to weight workouts, it doesn't matter quite as much if you do an endurance workout or heavy workout, because you'll gain muscle no matter what you do (in the beginning). Someone please correct me if I'm wrong.
For your money, Power Hour is probably the best value. It's an hour long and works every body part. Maximum Intensity Strength works the upper body first, then lower body last (maybe I have that backwards), so it's easy to split it into two if you want to do upper body one day, lower body the next. Power Hour intersperses upper/lower body reps, so it's not as easy to split it.
If you want the Pure Strength or Slow and Heavy series but, like me, don't have a lot of money to spend right now, you can obtain some of these series used from others on ebay, half.com, or the Firm Ya Ya's board (
http://pub109.ezboard.com/ffirmbeliversfrm13).
I've bought both the S&H series and PS series - they aren't here yet, but I can't wait to try them!!
Hope this helps. Good luck,