Ooooh sooo hard! YUI's version of Life was a favorite song of mine in December/January. I played it over 90 times in 2 months. Something I don't do too often, except for Ayu.
Life- Ayu version was very emotional. Another good song- Ayu never disappoints me, hmmm....it's weird....ha ha, but no complaints.
However, Mika's life was the best out of all three. Why? Because her song got me interested in Mika again. Yeppers. I love her version of life, it's very soothing. I've enjoyed that song for 8 months. It's a favorite.
Go Mika!