personally I haven't heard that many bad things about the shot. I actually urged my gf to get on it instead of the pill but she was more comfortable with the pill. It is my understanding that the shot has a better performance percentage and helps regulate mood swings and all the joys of pms. So no more cramping or bloating for her and no more being fussed at for you. On the other hand, she will also skip her menstrual cycle so that if it did happen that she got pregnant you wouldn't know until months into it unless you regularly cashed in and used a pregnancy test. Which isn't all that bad, but it's especially a risk if she's a drinker, cuz she'd be intaking alcohol without knowing she's pregnent.
The pill is fine but it's a bothersome procedure. You go to a pharmacy more often instead of going to a doctor like every few months or however often it is. (I might be pulling this out of my ass, but isn't there a 6 month shot?) Also, the first few months of being on the pill might suck for her. She may experience heavy, constant cramping, and may even skip her first period while on it.
the only one I know of by name is the depo shot.
hmm... all this talk about it makes me want to try to talk her into it again