I prefer the ESV. The NASB is rock solid as well. The KJV is perfectly fine as well, but I find it difficult to read since its written in Early Modern English.
My study Bible is ESV as well, so that's what I use.
You have to remember though that the Bible was really written in Hebrew, Greek, and Aramaic. So no English translation is going to do the best possible translation of every single word. I'm not necessarily saying its "wrong" to use a thought for thought translation either. I have when I didn't have something else available. I don't have a problem with the NLT for pleasure-reading (I used to have one as well.) But when it comes to serious study, it simply isn't as accurate.
Accuracy is based on two things, the quality of the manuscripts the translation was based on, and how the translation is done (Whether each individual word is translated, or each thought.) With these things, all I really know is what I've heard second-hand from people who have read scholars on the subject. To my understanding, the manuscripts used by the ESV, and NASB are considered more accurate than those used by the KJV and NKJV. But obviously other scholars think different. This isn't something that I know that much about.
But the KJV movement is crazy because they act as if God actually spoke English in the Bible! The bottom line is, first of all, the Bible wasn't written in English, and second of all, the KJV wasn't even the first English translation to begin with. So why is the KJV so special compared to other versions? It isn't.