Now, not ALL of Jehovah's Witnesses (I couldn't have better wording), just the sect and their translation.
To make it really quick, they change the Bible to agree with them when they find a contradiction, instead of changing themselves to agree with the Bible.
I'll do a comparison between NWT, NIV (http://gamrconnect.vgchartz.com/thread.php?id=191979), and KJV.
NWT: In the beginning God created the heavens and the earth. Now the earth proved to be formless and waste and there was darkness upon the surface of the watery deep; and GOD'S ACTIVE FORCE was moving to and fro over the surface of the waters.
NIV: In the beginning God created the heavens and the earth. Now the earth was formless and empty, darkness was over the surface of the deep, and the SPIRIT OF GOD was hovering over the waters.
KJV: In the beginning God created the heaven and the earth. And the earth was without form, and void; and darkness was upon the face of the deep. And the SPIRIT OF GOD moved upon the face of the waters.
NWT: Then those in the boat did OBEISANCE TO HIM, saying: “You are really God’s Son.”
NIV: Then those who were in the boat WORSHIPPED HIM, saying, "Truly you are the Son of God."
KJV: Then they that were in the ship came and WORSHIPPED HIM, saying, Of a truth thou art the Son of God.
NWT: In the beginning the Word was, and the Word was with God, and the Word WAS A GOD
NIV: In the beginning was the Word, and the Word was with God, and the Word WAS GOD
KJV: In the beginning was the Word, and the Word was with God, and the Word WAS GOD
(Note: The Word is Jesus according to John 1:14)
NWT: because by means of him all OTHER things were created in the heavens and upon the earth, the things visible and the things invisible, no matter whether they are thrones or lordships or governments or authorities. All OTHER things have been created through him and for him. Also, he is before all OTHER things and by means of him all OTHER things were made to exist
NIV: For by him all things were created: things in heaven and on earth, visible and invisible, whether thrones or powers or rulers or authorities; all things were created by him and for him. He is before all things, and in him all things hold together.
KJV: For by him were all things created, that are in heaven, and that are in earth, visible and invisible, whether they be thrones, or dominions, or principalities, or powers: all things were created by him, and for him: And he is before all things, and by him all things consist.