The bonus to the shot is that you don't have to remember to take a pill every day, or switch a patch every week or remove something from your V once a week...you just have to remember to get the next one...the downside is that you are stuck with it if anything goes wrong.
When I first went on birth control, my doctor's decided the shot was not a good idea because of my diabetes. If it effected my diabetes in anyway, I'd be stuck with it in my system.
Instead, I went on a low-dose pill for about...6years until it finally wasn't working for me(caused me morning sickness) and I switched to the birth control patch which I've been on for 2years and love. I just replace the patch once a week and forget about it. You keep it on for three weeks and then have a week off.
There's also the Nuvoring (probs spelling that wrong), which a friend of mine has and loves, which you also remove once a week(or maybe it's once a month...) and keep in for three weeks and a week off.
If you really want something you don't have to remember though, maybe check out the IUD? My friend has one and hasn't had any problems with it, but at least if something were to go wrong, it could just be taken out.
I had friends when I was in highschool who got the shot..one of them went totally insane for a year. PMS 24/7. it was horrible for us and her. Another one of my friend's had her period for months at a time when she got the shot. My friend who uses the Novoring used to take the shot and didn't have any side effects(that i'm aware of) but decided not to continue with them after highschool.