What's better: pills or injections?

Giovana • I'm a fucking enthusiast.
I'm a pill user for 5 years already but always felt curious about the injections methods. What I'm insecure is if they are as much as effective as the pills, since I want to avoid the forgetting issue with them.
I've heard that you can take it one time per month or three months, something like that. But how effective is it, anyway?
Cheers.