I use to get the shot years ago... after having the 5 yr arm thing removed (which was recalled - btw). I know there is a new version of the arm thing, but my doc doesn't recommened it because it is new and what most of us went through with the first version.
Anyways, the shot worked every well for me. Personnaly, I didn't have periods when on it, minner spotting when it was about time to get another one. You do have to get them every 3 months. I use to get mine in the upper butt because if I got it in my shoulder where they like to give them my arm would freeze up & I worked in a factory at that time - so I couldn't have that. I did carry more weight when on any kind of birth control... but it didn't matter what kind, they all did it to me. The only other issue I had with the shot is the amount of time it takes to get "out" of my system. I stopped getting it in 2000 and didn't get pregnant till 2003 - but I also have POS, so that could have a major play in that too. But with the pill... I can be pregnant within just a few months of stopping it & have 2 and one on the way to prove that.
Good luck in choosing - sometime I think it's hard to choose a Birth Control method... there are just so many of them.