The first English translation of the Bible was Wycliffe’s translation of 1382. The first English Catholic Bible was the Jesuit Douay Rheims Version of 1582.
An important thing to keep in mind when studying this topic as that THERE ARE NO ORIGINAL MANUSCRIPTS!
There are two MAIN lines of manuscripts from which Bible's come. The most famous of the corrupt strain are Vaticanus and Siniaticus. However both of these are late, compared to the Old Latin and Old Syriac Peshitta, both dating back to before 180 AD, according to the International Standard Bible Encyclopedia.
Augustine commissioned a military crusade to replace the Old Latin Bibles of the Waldenses living in the Alps with Jerome's Latin Vulgate. The different Bible was giving Rome a hard time maintaining control over outlying Christian groups. The Old Latin readings were perpetuated by Christians who were being persecuted by Rome. Under cover, these manuscripts, reflecting the Byzantine type text, were perpetuated by God fearing Bible believing Christians at the cost of life limb and torture and much blood at the hands of the catholics. These readings came to be known later as the Received Text. Erasmus compiled, edited and published a Greek New Testament from these more reliable readings. Other English Bibles arose from this text, such as the Great Bible, the Bishop's Bible, the Geneva Bible, Tyndale's translation, and finally the King James Authorized Version of 1611. These purer texts were also the ones used by Calvin, Luther, and Zwingli, and it is what spawned the reformation against Catholic paganism.
During that time period, most Christians understood the pure texts verses the corrupt texts used by the Catholics. The readings of A (Siniaticus) and B (Vaticanus) were available to the Reformation translators, although the actual manuscript of A was not discovered until the 1850's in a trash heap in a monastery on Mt. Sinai. However, there is nothing in them that is not already represented in the Vulgate.
These corrupt readings trace their roots back to the corrupting (2 Cor. 2:17) efforts of Origin in his 6 column work called the Hexapla which contained several biblical and pseudopigraphal writings, though greatly altered. Because these were transferred to vellum in Vaticanus, instead of Papyrus like the pure text, scholars mistakenly believe these to be more reliable. However, the main two manuscripts for the Catholic Bibles disagree over 60% and contain many gnostic materials, as well as the apocrypha. The Received Text papyri numbering well over 5,300 agree over 99%.
Since 1611, no Bible believer has had a need to redress the translation Issue. In 1881, Westcott and Hort reintroduced the Catholic Bible readings after the discovery of A, taking advantage of all the publicity. What seemed hopeful, was unfortunately a marred attempt to replace the protestant Bible with Catholic readings based on incredibly poor scholarship.
Today, all the new version that come out are based on the scholarship of Westcott and Hort. Therefore, all the new versions, are simply the Catholic Bible minus the apocrypha.
The NIV is simply a modern Jesuit Rheims version from 1582.
To illustrate some of the differences numerically:
There are 64,098 fewer words in the NIV than there are in the KJV.
There are 17 complete verses missing, over 220 partial verses missing, and there are over 30,000 changes that affect the meaning of the text. If you were to combine all the missing material, it would equal the length of 1 & 2 Peter.
For examples, check these verses and compare them:
Matthew 17:21
Matthew 18:11
Matthew 23:14
Mark 7:16
Mark 9:44
Mark 9:46
Mark 11:26
Mark 15:28
Luke 17:36
Luke 23:17
John 5:4
Acts 8:37
Acts 15:34
Acts 24:7
Acts 28:29
Romans 16:24
1 John 5:7
More information can be found at these websites:
http://www.deanburgonsociety.org/KJBible/answers.htm
http://www.biblebelievers.com/BibleVersions.html
http://www.fundamentalbaptistlinks.com/kjv.htm
If ease of reading is your primary concern, I recommend “The Defined King James Bible” which has definitions for uncommon words in the margin where they are easy to find. http://www.biblefortoday.org/kj_bibles.asp