Q: I have 163.4 pounds of lean body mass and my sister's lean body mass is only 110 pounds so my Basal metabolic rate must be faster.

A: In that case probably yes, her BMR is lower than yours. It may not necessarily be so since BMR is influenced by a ton of factors and is not just proportional to the lean body mass, but I would agree, that yes, yours should in general be higher than hers. However that alone does not lead to the conclusion that your muscle mass makes you gain fat or that it does not help you lose fat. If you wanted to compare the effectiveness of cardio vs. weight training + diet in helping you fight fat, you should compare it against yourself. For example, follow a weight training + diet routine for 6 months. Then follow a cardio routine for 6 months. Then compare the results. Even then the results won't be very accurate because it's always easier to lose fat in the beginning when you have more of it, than later on (so whichever program you follow first will have a big built-in 'advantage').

I always insists on combining weight training with diet because weight training will raise your metabolism and will make you hungry. If you're not sticking to a diet, it's very easy to overeat while weighttraining because you're feeling hungry much more. This is a common reason why people may not have the success losing fat through weigh training that they should -- they simply eat whenever they're hungry. If you do stick to a good diet, so you don't overeat, weight training will bring you much faster results.