hit it right on the head - reps vs. weights actually target different aspects of your muscle development. So really, the answer to your question depends on what exactly your goals are.
There are a few threads in the weight lifting forum as well right now, discussing different rep/set patterns for different goals and how muscle/strength develops. In terms of healthy muscle/connective tissue development, a 'bit of everything' tends to work quite well.
To add to what nelie
said: strength has to do with your muscles contracting with more force
, whereas endurance is about them contracting for longer
. The two aspects actually use different metabolic pathways in your cells (aerobic vs anaerobic). Mid-high rep schemes (ie. ~8-15 reps for women) will also cause some hypertrophy (muscle growth). Low reps (3-8) aim closer for strength, and higher rep sets (15+) develop endurance.
I like to think of strength as picking up a toddler vs. endurance as holding the kid for 2hrs.
I'll also mention for Mad Donnelly
: A) kudos for not worrying about looking like a bodybuilder! and B) take a look at your training progression, and maybe ask yourself how much direct ab/core work you actually want. While women don't put on upper body muscle as quickly as guys, we're still very capable of growing, especially in body parts that we work - it's very possible that you could increase your waist circumference from ab/oblique exercises (not sure if that's a concern/goal, but it's worth mentioning just in case