Usually, I choose the best answer + i also click on "helpful" on the other answers. Because it's also unfair that someone who wrote 10 lines explaining grammar and everything, doesn't get more attention than someone who "only" corrects your question. If all answers are the same, i don't choose any "best". When i answer a question, it's important for me if someone says my answer is the best. Not because i want to be the best or because of ranking, but because i'd like in some years to follow a training to become french teacher for foreigners. I'm also tutor for foreigner in my university. If here people think i'm good in explaining, i can continue this way to explain, if it isn't, i have to improve, to become clearer so that people who ask can improve too.

I don't choose it right away, I wait until a lot of people has answered my questions because if you choose the best answer no one else can add more answers I just click on helpful.

If I think the answer is most correct i will give the best answer to him or her.