Choose an option from the poll. 
What does “best” mean? Most effective? Most convenient? Most available? Cheapest? Least side effects? Least instrusive on sex life?
Abortion. Definitely abortion.
Well, since this poll is in the “In My Humble Opinion” forum, I would assume that you are basing your option on your opinions after you have weighted all the benefits and downsides of each option. Also, please note that it is a multiple-choice poll, where you have multiple choices and can choose more than one choice. So, whatever is most effective, most convenient, most available, cheapest, carries the least side effects, or less intrusive on sex life, in your humble opinion, with your reasons, should be chosen. The reason why I put it here is that I realize this is a very subjective subject, and people do have different measurements (as you have pointed out) to weight certain choices over others. Because people are using different measurements, the interpretation of the word “best” is most likely going to be different, from individual to individual. One person may find this choice to be the “best”, because it suits his or her needs and desires, whereas another person may find that choice to be the “best”, because it suits his or her needs and desires.
I wish to register a complaint – well, really point out a flaw – in your poll. You ask for “the best” but then give us the option to choose more than one.
Therefore, I choose that they are all equally the best.
Don’t you kneed aspirin on there?
Wow, total abstinence is off to a strong start. While I agree that’s pretty effective, for a lot of individuals and couples alike it’s not very practical (read: likely.)
The best form of birth control is whatever works and will be used by the couple (or triple or whatever) in question.
For my partner and me, it’s a combination of FAM and withdrawal and outercourse, only two of which are on your list.
Anti-what vaccine?
Well, it obviously depends on how the voters are defining “best”. It absolutely works…it just doesn’t lend itself terribly well to actual, y’know, sex. 
As far as I know, this has never reached the stages of human trials in the US, much less been approved by the FDA. I believe India was the hotspot for this public relations disaster. I don’t know if it was ever approved there.
Having a couple kids of your own.
Once you realize that each one will cost about a quarter of a million dollars to raise to maturity, it moderates your behaviour.
One Doper voted for each and every method, including both abstinence and withdrawal. Makin’ a point there, dude?
Sort of …
I always thought that both parties going to college was the best way to reduce the overall number of babies. Education rocks.
Best form of birth control = abstinence.
Best for of birth control while still engaging in sex = whatever the person in question will actually use.
I was on the pill until I decided to have a kid. After having my son, I used fertility awareness/natural family planning methods for 4 years. When I realized I didn’t want any more kids, I had a tubal ligation.
All three of those methods worked perfectly for me, especially the last one.
There is no flaw. “The best” can mean one individual object or one set of individual objects, such as “The Best Schools”. And yes, I give you the option to choose more than one option, and you do so accordingly, which demonstrates that all of the options, in your opinion, are “the best” and none is the worst.
Nope. The best would be suicide. There are however side effects.
Well, I was mostly just joking around, because of the whole superlative argument. Only one thing from a list can be the best thing (unless there’s a tie, I suppose). It’s like something being described as “most unique.” There are no degrees of “unique” or “best.”
However, I did choose all, and I did proclaim all to be the best, and, by extension, none the worst, and then my Rhetoric professor from college dropped by and had me flogged … but mostly for comma abuse.
If you dont have sex you wont get pregnant. 100% effective
Your face.
Ohhhh, snap.
eta: generic you. Not directed at anyone.