Condoms: FUCK YES, BUY CONDOMS. More importantly, weird as this sounds, after buying a pack, masturbate with one on. Condoms are 96% effective IF USED CORRECTLY. If you're slightly too thick for the size you have, shit can and will break, making all your preptime pointless. If you're too narrow, the thing can slip right off without you noticing, and BAM, you might as well have gone catholic mode. Having the right size of condom isn't as important as having one in the first place, but it goes a long fucking way. BONUS: Condoms are one of the few birth control methods that keep your "virgin, I swear" new girlfriend from giving you all the shit she caught from the last guy she told she was a virgin.
The pill: Shit, let's get it out of the way now- IF USED CORRECTLY, birth control pills are 96+% effective. Notice, this is a form that requires no input on your part, but you have NO CONTROL OVER. If your girl misses even one pill, the hormone cycle can go completely off, making her possibly fertile for the next 3 weeks until shit gets all settled again. Before you rely solely upon the pill, ask yourself the following questions:
1: has your girl ever forgotten to do/take/retrieve something that she needs on a daily basis, like her keys, bookbag, purse, wallet, credit card?
2: has your girl ever lied to you or delayed telling you about something she deemed inconsequential, but was in fact very important, like encountering ex-boyfriends when you weren't around, money issues, damages to things you own, etc?
3: has your girl ever looked at an infant and reacted very positively with no provocation, with signs including cooing at the baby, smiling like she just won $100, wanting to hold the baby?
If you can answer yes to ANY of these questions, DO NOT RELY SOLELY ON THE PILL. Even if she doesn't mean to, your girl may mess up her cycles, and it can cost both of you dearly.