Well abstinence is always going to be the safest but it's just not realistic to expect that of everybody who doesn't want kids yet. Also it depends whether by safest you just mean the most likely to prevent unwanted pregnancy or if you're talking about also preventing STI's. Hormonal contraceptives and sterilisation won't help with the latter. For that you need a barrier method like condoms. And of course you can use more than one method at a time, like the pill and condoms in combination.
Well, I am not a doctor but I feel that since no method is fool-proof then one can choose to adopt more than one method. For example, one can take the contraceptive pills regularly and ask the partner to wear condoms as well to ensure double protection.
Contraceptive pills have a number of side effects however, taking occasional breaks from the pills while continuing the condom usage can supposedly negate some of the side effects of the pills.
I'm personally doing abstinence at the moment, and is what "I'd prefer - no medicines and pills; however condoms have been effective in the past. Have been on the pill, and although it regulates the menstrual cycle and gives you clear skin; the other side effects are unpleasant, and not worth the benefits. Have tried Implanon. The latter is a fantastic set and forget form of contraception; however that "time of the month" can strike at anytime without any warning.