The first version of the YS that I read was The Essential Yoga Sutra: Ancient Wisdom for You Yoga translated and commentary by Geshe Michael Roach and Christie McNally. This is the version I got in my 200hr, and I find that this version makes a good attempt to make this very abstract text more concrete. It contains both the Sanskrit and the English as well as plenty of commentary.
The second translation I use doesn't have any commentary, but it does have a direct word for word translation. It's also online, which is a plus. I was provided this version for my course on Hinduism.
http://www.light-weaver.com/ys/ysp-skrit-eng-chip-hartranft.pdf
I also use Geshe Michael Roach's How Yoga Works from time to time, while I find that the 'translations' provided are usually pretty far off the literal translation, because the book basically explains the main points of the YS through a narrative it's really easy to get your head around.
And fun bonus for the real nerds out there, a recording of the whole YS chanted with a student and teacher (which blogger won't let me embed for some reason):
http://www.youtube.com/watch?v=WzCrhOPxt6M
