How Many Sets and Reps for Strength, Mass and Endurance?

Answer:

For strength, your best bet is low reps (2 to 5 per set), long rest periods (2 minutes +) and low volume (e.g. 3 to 4 sets).

For muscle mass, moderate reps (6 to 12 reps per set), moderate rest (1 - 2 minutes) and moderate to high volume, depending on intensity (5 to 8 sets).

For endurance, high reps (15+), brief rest (30 seconds to 1 minute), and moderate to high volume (5 to 10 sets).

These are VERY general guidelines, keep in mind. The specifics of a program will vary a lot.

I find both approaches to weight that you mention work well.