The only difference is in spelling and printing errors that were corrected.
Thus, you may use either with full confidence you have the pure words of God.
The Greek and Hebrew texts underlying the 1611 has never be changed unlike the modern versions which are always changing their readings.
Last time Nestles had to reinsert 300 readings from the Receptus showing that the King James had been right all a long!
I don't mind the KJV -- but it is not superior to any other good translation (NAS, NKJV, and to a lesser extant, NIV), and it is certainly not superior to a study of the autographs, which we can say we have with a reasonable degree of certaintly.
The Greek text underlying the KJV was Erasamus's NT. A brilliant work of scholarship in its own right, to be sure, but limited because of the challanges Erasamus faced in getting manuscripts. For instance, he had to back-translate from the Latin Vulgate certain portions (shooting from the hip, not quite sure which portions). He did a respectable job, but archaelogy marches on -- and more MSS'es were found. They generally vindicated Erasamus, but in other areas revealed a better rendering.
God did not speak in the noble prose of 1611 (or 1742) King James English, but rather the earthy, easily understood common Koine greek. If God were to inspire the Sciptures in the intellectual Attic Greek, then we might have a leg to stand on for the KJV-only position. But he used the common language-- and why should we do any differently?
This new-age conspiracy crap of Riplinger et al. is certainly not correct. It is based on ignorance, misplaced fears, shoddy scholarship, and blatant mischaracterizations and slander. Unfortunately, Evangelical Christianity has overreacted to the excesses of higher Criticism and thrown out the proverbial baby with the bath water.
I myself use both the KJV and the NASB. Generally, I like the NASB translation because it is easier for exposition to others -- I'm not translating what the archaic English means. But I'll be the first to admit that I don't care for every translation of the KJV. There are some that are just unfortunate. But the same may easily be said of the KJV.