There can be alot more than just the various translations, also something to consider is the Greek/Hebrew/Aramaic behind the various verisons.
there are different texts of the original langauges that are used to translate the Bible into english. The King James Bible uses what is called the Received Text/Textus Receptus.
Most new translations use what is called the Critical Text.
there are other "families" of text, such as the Majority text and such.
Opinions vary about which is closest to the original Scriptures, the Critical Text or the Textus Receptus, i have been looking into this, i still have questions, but i agree that a Bible based on the Received Text is the best to use as a main Bible. the KJV is built on this, and if you can understand the KJV, then there is no reason to stop using it, however as other suggest i think using more than 1 translation can be useful.
if you want to look into the different text basis you can search/google Critical Text or Received Text and such and come up with alot of info, not all of it useful.
when looking at different Bibles though realize that some differences are due to the different text used, such as it would appear that the body text of the NASB takes out some of 1 John 5:7-8, it looks like it does footnote it though.
Biblegateway.com is a site i use to check various translations, if you want to you could look at the different verses there and see how they read.
i am not sure how crucial the issue of the textual basis is, such as if something is basedon the Critical Text or Received Text, and i cant properly explain them probably, but i figure if i can read one that is closer to the words the authors wrote, that God inspired, why would i read a different text?
i also agree with literal translation, word for word, is best, not what someone decides is the thought that is trying to be communicated.
the NKJV, is said by some who are for the Received Text, to not be the best Bible because of its footnotes that show the different manuscript variations, and that the OT text is different than the one used in the KJV, and other reasons.
in my understanding there are also the MKJV and LITV, KJ21 which are Textus Receptus/Received Text Based
i cant really explain, i would use a Received Text Bible, such as the KJV as your main Bible, and with understanding some differences in verses its not bad to see how other verses translate things.
you can also go to blueletterBible.org
and go to a verse, there are buttons by the verses, one with a "C" on it, this will take you to a lexicon for the original langauge, and you can without knowing any Greek/Hebrew/Aramaic see different definitions or way of using the word behind the translation.
although im not sure if those are the best lexicons/dictionaries for those words.
above all, trust Jesus, and the Holy Spirit who teaches us the truth of all things
1 John 1:9 KJV
9If we confess our sins, he is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness.
thank you - jason