Hello Faithwoman,
After several questions to many pastors and biblical scholars, they all agree that there is no 100% perfect translation. There is basically two categories. Literal and Dynamic. Your King James is a more literal translation but some of the context of the grammar is lost. Your NIV is a more dynamic translation meaning that the translator attempts to fill the time gap to make it easier to read. Both versions are fine. I recommend that you pray about it and let GOD show you what he has for you in this specific time in your life regardless of the version you choose. I found some very good computer software called E-Sword. There are many free bible softwares and E-Sword allows you to download several versions of the bible and put them side by side to do a comparison while you read. I use that extensively in my bible study. I am currently using the NLT (New Living Translation) for two reasons, 1 my pastor at church teaches from this version and 2, it is easy to read. I keep a King James and a New King James handy for reference though
Bottom line is find one that suits your study needs and one that speaks to you spiritually. Trust that GOD will lead you where he needs you to go.