I slimmed down all over - remember, when you lose fat you lose it all over - there's no such thing as spot reducing. Also that's why I can't really say whether elliptical or treadmill is better for legs. I think it depends on the person. I, for example, can't run very long and my knees are sensitive so I try to stay away from the treadmill (unless it's for short runs/inclined speed walking). Also, I think the resistance training really helped a lot. If you do too much cardio without resistance muscle building then you lose your muscle together with the fat and that's never a good idea. So, provided your doctor/trainer says it's ok, do some weights too!
I've heard that swimming is great exercise and I think I found out for myself yesterday. I went for a short swim in the afternoon and wow I can feel my muscles really working hard!
If you only plan to go to the gym once or twice a week then you can still do other things on the off days, like walking, or swimming.