OK I am eventually (God willing) going to become a bible translator for wycliffe bible translators. If you don't know what they do, just type wycliffe into google and depending on your country there will probably be a wycliffe site for your country.
Hopefully I have learnt enough to say a little about this topic. All translations errors. All of them. I am yet to see an infallible version. The original Greek and Hebrew aren't even perfect because there is a dispute over which manuscripts are correct etc.
All translations have errors. There are two major ways of translating the bible, word-for-word, or idiomatic translations (or a mix of both).
Word-for-word is very obvious. It is a translation from Greek, Hebrew or Aramaic into English or whatever other language. Word-for-word translations at first seem like the obvious better option. We are getting a direct understanding of what the original authors intended. However, as somebody has said, many find the New King James version difficult because in the change of the style of language used. if the KJV was written 1611 (sorry if this date is wrong) and a change in language has occured, imagine how much has occured since the time of the NT or even the OT writers!
Idiomatic translations attempt to solve the problems caused by differences in language styles. For instance, somewhere in the OT (forgive me, I can't remember where) the original Hebrew says that two people were having a heart-to-heart conversation (I am pretty sure it was heart). Now most people in our society would assume that means an honest discussion, but to the people from the OT, this was an IDIOM, for a deceitful conversation, the exact opposite!
Word-for-word translations are helpful for the studier of the bible, when you have time to site and research the meaning and have a constant understanding that the meaning could very well be different to what it appears.
Idiomatic translations are good when you need to understand quickyl what is being said.
As I said before, both have faults. Wycliffe bible translators use a mix of both to translate the bible into other languages, and it an take up to 30 years or more to get the translation correct.
KJV is a word-for-word
NIV is a mix, but generally idiomatic.
I personally use NIV, many use NASB because it is the most literal word-for-word translation in English. I'm not here to make a decision for you, I just thought it might help if you understood a bit more about the translation process.