I now mainly teach teenagers and non college educated adults. We can use the ESV, read the Bible, and the reading is easily comprehended. They may not know the theology of the passage, but they at least comprehended the wording.
We try the same in the KJV and I spend more time explaining the language of the passage than the meaning of the passage.
You make an excellent point concerning the difference between using modern English vs. the antiquated English of the KJV! That single point alone make nearly any modern translation superior for use by newer Christians who are just trying to learn the basics.
However, there are real problems with the source material for nearly all of the modern translations like the ESV and NIV, etc. to the point that, for anyone doing serious bible study, who wants to get into the deeper details beyond what would be typically taught to laymen in a Sunday school class, these translations are prone to lead people into serious error and should be avoided.
For most of the reasons given so far in this thread, as well as many others, what are referred to as the "Majority Texts" is superior source material and, since modern English is clearly superior to a centuries old form of English that no one speaks any longer, the clear choice for the serious bible student is the New King James, along with a healthy understanding of, and frequent reference to, the original languages, of course.