Slowly move away from the machines....
The high rep-lower weight vs. higher weight-lower rep issue really isn't a debate at all. It is a question of what are you training for? Muscles respond differently to different types of training.
Keeping reps in the 10-15 rep range is good for striking a balance between training for increase in muscle size and strength. Rest for 40-60 seconds between sets or super-sets. As a woman, if you have fairly normal hormones, you aren't going to develope huge muscles, so don't worry about looking like Mr. Olympia himself.
If you want to train for sheer strength like a power lifter, keep your reps under 8, generally doing sets of 8-6-6-4 with 2-3 minutes rest between. This method of training will develop larger muscles, greater strength, and is incredibly BORING. Very effective if you are going to enter a bench pressing competition, however.
If you are training for endurance, and do not want to build muscle mass (you are a marathon runner and can't afford to be toting along ANY extra body mass) you would want to go with higher reps and lower weights. Up in the 20-30 rep range. You will build some muscle, but you'll mostly be building endurance.
Another way to train is to mix it all up. Do pyramid sets (8-10-12-15 reps), drop sets (reverse), train high volume-low weight one week and high weight- low volume, the next.
So the debate isn't "what's the best way to train", but "what is my goal in training?" Your body will react differently to different types of training. The same goes for doing cardio. If you practice doing 100 meter sprints with long rests between each, you are not going to do real well at a 10K race. If you train doing paced distance runs, you aren't going to be a good sprinter.
Pick your goals, then train to meet them.
For overall conditioning, body sculpting and weightloss, I'd recommend staying in the 10-15 rep range, lifting as heavy as you can, incorporating supersets, and
move away from the machines! Ilene is right- a lot of them just can't be adjusted for small to mid-sized women. If you have 1 stronger side (and everyone does), they don't help you develope a symmetrical physique. They don't help you develope balance or core strength. You'll eventually get really bored with the scope of the workouts that you can do on them. Find a knowledgeable trainer or gym buddy to show you proper form on some free weight exercises. They really are more fun
Mel