I chose the ESV because if I could choose only one Bible to use for devotional reading, study, preaching, and teaching, the ESV would be my preference.
I like the fact that the ESV sticks firmly to formal equivalence without becoming excessively wooden like the NASB, which would be my choice for study.
Whenever I get the opportunity to preach or teach, I use the NIV because the vast majority of the congregation uses it. However, I would gladly replace the NIV with the HCSB, for I believe that it doesn't flirt with paraphrasing like the NIV does at times. Additionally, the HCSB has EXCELLENT footnotes which provide literal renderings of many, many verses when the translators felt that the main text should be more dynamically equivalent than formally equivalent. I've been using the HCSB for devotional reading lately.
However, if I MUST choose only one, I'd go with the ESV (or maybe the HCSB, but it wasn't on the list).