"Several versions" is a bit of an overstatement.
First, ignore anything that's not written in Hebrew/Aramaic (for the Old Testament) or Greek (for the New Testament). Anything that isn't in the original language is just a translation and by its nature not definitive. There are some extremely good translations and there are some pretty poor ones too.
In the original languages, the definitive Old Testament is the Masoretic Text. In the New Testament it's a little more complicated - the 1611 King James ('Authorised Version') is based on Textus Receptus, whilst most modern translations are based on NU-Text. In practice there's no significant difference between the two, just a few words here or there and nothing that changes any aspect of doctrine.