Q: My sister's Basal metabolism is much lower than mines but since she is much more active than me It is easier for me to gain weight than it is for her. I know certain people who do only weight trainig because otherwise they would be fat cause they are basically couch potatoes and dont like to play sports or do any kind of cardio.

A: I wouldn't read too much into the fact that you put on weight faster than your sister. You are two different people and your bodies work differently. Your diet is undoubtedly different, as is your activity level. You do not know that your sister's BMR is lower or higher than yours unless you ran a controlled experiment to determine it. Basically it does not mean anything that you gain weight easier while your sister is more active.

Not really sure what to tell you about the second part either. Yes, many people who weight-train would have more fat than if they didn't weight traing. But that's the whole point of weight training to lose fat, right?! I'm guessing that you want to say that cardio is better than weight training and you are entitled to your opinion. I think cardio is great for you and everyone who can should do it. But cardio, especially excessive cardio, is not the most optimal way to burn fat, certainly not as good having a good diet and weighttraining program. I will agree with you that too much of cardio is still usually much better than no exercise at all.