They are both important, even if you do have a tendency to bulk up a bit-- I know I do. But weight lifting can be used to firm the muscle only, which helps keep the skin tighter as you lose, and keeps you from jiggling as much. More muscle also helps get your resting metabolic rate up, which burns calories. Try lifting lighter weights, for more repetitions, and fewer sets. Don't max out in areas you don't want to get any bigger.
Cardio is mandatory for heart health, hence the name. It increases your lung power and endurance, so everyday life is easier and less stressful. It also strips fat fast, which makes bulking up less of an issue. In my experience, I look bulkier when I build muscle faster than I lose fat, so the total mass is greater than it was before. If I do cardio and weights, I can keep the whole process moving toward my goal: firm AND sleek, trim AND taut.
If I were pressed for time in my workout, I'd have a trainer design a cardio and circuit weight training plan for me, say 30 - 45 minutes cardio 3 times a week, and a weight circuit 2 - 3 times a week. You might want to consult with a trainer in your gym for an opinion. Good Luck.
Age 48, 5'6" Living with PCOS.
Start: January 1, 2002, 220 lbs., size 24
Current: 163 lbs, size 10 - 12, 39"-31.5"-39.75"
Goal: size 10 in Levi's 515 jeans.