NASB - word for word translation. Places a greater emphasis on word conversion than format and therefore tends to be more difficult reading. Excellent source for Bible studies in general.
NIV - meaning for meaning translation. Places a greater emphasis on intent. Definitely an easier read. Prime candidate for all of the reading through the bible programs. Also helpful in studies where the language is going over your head from an NASB as the NIV can better contextualize the concepts.
KJV - best version for structural format. In a passage of several verses...sometimes it can be difficult in determining what the author was trying to emphasize. In those cases, the KJV does an excellent job adhering to emphasis via word placement and sentence construction.
ESV - attempts to hybrid the 3 above.
Bottom line...make sure you are in one of them daily. And if you ever feel like you have to champion one more than another...champion the original text and learn Greek & Hebrew.
Elusiv