If You Could Only Take One Supplement, Which One Would You Choose?

I'm really curious to see what other people would post. I sometimes wonder about this because supplements are very expensive. It is very conceivable that I will someday have to make this choice for myself and it's a huge dilemma. I love my supplements because they have helped me feel so much better.

Please everyone, share your thoughts on this with me.

If you can't choose just one, then pick the top 3 that have helped you the most and why.