I have tended to prefer the NASB, but I got into the ESV for the reason you cite-the Reformation Study Bible.
I was NASB for nearly 20 years. I switched to the NKJV only because I acquired a Reformation Study Bible about four years ago that was NKJV. At the time, it was going out of print and prices were good. I picked up a new leather-bound with thumb index version for less than $50, and liked it so much I bought a second-hand hardbound version for under $20 (it's only defect were the coffee stains on the page edges) so I wouldn't feel guilty in marking it up.
Just this month, I picked up a pocket-sized ESV (OT and NT)for my briefcase (Family Christian Bookstores, member-only table item for $5), and I have to admit that I really like the translation. I can see why it's popular.