The Authorized Version of 1611 (King James Version) utilizes the Textus Receptus ("Received Text") as the basis for the Greek New Testament. The Textus Receptus is based upon various Greek texts as well as some influence by the Latin Vulgate. The earliest work being prepared by Desiderius Erasmus, revised by Robert Estienne (better known as Stephanus), and further revised by Theodore Beza. The text produced by each, is substantially the same, there are some variations between their various editions.
The Blue Letter Bible utilizes the Stephanus 1550 edition.
Many of the newer translations are based upon Alexandrian texts. The Blue Letter Bible also provides the Greek text based upon such Alexandrian texts, noting however that the King James Version is not based upon such texts. The Alexandrian based text that is shown is the combined Westcott-Hort / Nestle-Aland 26th edition variants.
The Blue Letter Bible has purposely not made a statement of belief as to the priority of one text over the other. While we feel that there are many good scholarly debates that exist, we generally see that there are also many debates that are divisive of the Body of Christ. We therefore leave that decision up to the individual, and suggest that they pray about the situation and ask the Lord Jesus Christ through the Holy Spirit to provide the answer to their questions about this issue.