The Canadian Pediatric Association is now recommending IUDs as the best/primary birth control option for teenage girls. This seemed surprising until the CBC story explained that IUDs are the most common form of reversible birth control in the world, with the exception of N. America (and also that, in real world use, the pill has roughly a 9% failure rate due to user error).
http://www.cbc.ca/news/health/birth-control-iud-1.4684855
Still use condoms, though, to prevent STIs.