I had a really bad time with weight gain and especially losing weight while on the pill. The gain I attribute to the fact that my appetite was ravenous while I took the hormones, but they also made it extremely hard to lose weight. I could eat nothing but a piece of fruit every day and STILL gain weight on the pill or nuvaring. I also had a lot of other severe emotional problems, acne like a 16 year old, alopecia, complete lack of sex drive, the beginning stages of osteoperosis and not being able to absorb nutrients, etc while on them.
Some people are really sensitive to hormones, like me, and even the tiniest amounts mess them up pretty badly. Hence why I have a Paragard, which is the copper hormone-free IUD. I've had it since October and I love it.
A lot of other women have no issues with hormonal birth control at all, except controlling their eating while on it. However, don't take the BS excuse that, "it's not the birth control." All of my issues -- even ones I hadn't attributed to B.C. -- went away in the months after I stopped using hormones.
Listen to your body before you listen to what someone tells you, and note that it sometimes takes years to notice side effects and changes. Good luck whatever you decide, though.