There are a lot of translations available today, and it is helpful to know how they are different and what they have in common. In terms of understanding broad categories, there are two basic things to know about Bible translations. One is their source material, and the other is the translation technique used.
Taking the latter factor first, there are three basic categories of translation techniques:
In a word-for-word translation for every word in the source text, there is an attempt to have a corresponding word in the translated text. These are often described as literal translations. The more frequent the correlation of words from source to destination, the more literal the translation is. The KJV, NKJV, NASB and ESV translations would be in this category.
In a phrase-for-phrase translation, there is not a commitment to have a word for every word, but translators do try and translate every phrase from the original text. Given how different languages can be in their grammar, this technique can greatly increase the readability of a translation. Many people prefer this kind of translation for maintaining a daily Bible reading habit. The NIV and NLT would be in this category.
Then there are paraphrases. These are not really Bible translations in the formal sense of the word. They are more texts based on an original text or another translation with the writer taking extended liberties to bring the ideas and stories into a contemporary context. (NLT does a little of this by converting dates to the Gregorian Calendar, but for the most part it is still a phrase-for-phrase translation as far as I know.) The general idea behind a paraphrase is to bring a fresh perspective to the text. The Message is a widely-known paraphrase today.
All Bible translations find their origins in one of two strains of original manuscripts. One is the Majority Text, and the other is a text with principles of textual criticism applied. While most manuscripts are largely consistent, especially in vitally important areas, among the 31,000-plus verses in the Bible, there are around a couple hundred times where in a minority of the manuscripts small parts of the text are absent or added. Textual criticism considers factors and often decides to leave out missing parts of the text, ignore anomaly additions, and sometimes assumes things like repeated phrases were copy errors and leaves those out, too. The resulting operating text under this method from which translators work is sometimes called the Critical Text or “earlier texts.” (Yes, Bible translation work is included among “every labor and every skill” in which there is “rivalry between a man and his neighbor” or fellow Bible translator, to add paraphrasing to Ecclesiastes 4:4, NASB.) That's my basic understanding and enough for my purposes here. I'm sure Biblical scholars can fill in holes, correct me, and illuminate oversimplification as they see fit.
For purposes of memorizing Scripture and deciding on a translation, I first wanted to know which translation came from which text. I knew the Authorized King James Version (KJV) came from the Majority Text and wanted to know which others did as well. When I started in 2006, the New King James Version (NKJV) was about the only contemporary Majority Text-based Bible translation. Another Majority Text-based version that was finished in 2012 is The Voice. (That one is unique in that it is probably closest to a phrase-for-phrase translation with possibly some NLT date-style updates to the text or modifications to how names are translated. I don't have a copy, so I haven't read it yet, but there are definitely some things about it I find fascinating.)
All other translations are based on the Critical Text including literal translations like NASB and ESV and phrase-for-phrase translations like the NIV and NLT. Originally these translations were printed with verses missing, and some still are. When the NIV came out in 1984 with Matthew 18:11; Mark 9:44,46; Acts 8:37; and other verses missing, this caused concern for many, especially considering the severe warnings in Scripture “if anyone adds” or “if anyone takes away from the words of the book of this prophecy” (Revelation 22:18-19). I am not here to pass judgment on anyone who prefers the Critical Text or any of its descendant translations; that is for God to decide. These days no matter which source text a publisher is using, they tend to include notes about parts of the text that are or or not included in the other original text.
As a practical matter, in recent years I met someone who had memorized the entire book of Hebrews in the NIV, and afterwards he regretted having used that translation. He later memorized Scripture from the ESV. That's still not a Majority Text translation, but it is far more literal translation than the NIV. I also find that the less translators are committed to writing a literal translation, the more words they end up including in their result. Unnecessary extra words are not my objective in memorizing already long passages of Scripture!
Based on all I learned about the texts, I decided I wanted to memorize a literal word-for-word translation based on the Majority Text. If I am going to put in this much work to memorize Scripture, then I want to make sure I get as much value as possible from committing to memory words that are as close as possible to the originally inspired words. That quickly narrows translation options down. My other method for deciding on a translation was to simply read the first part of Romans and some passages that clearly present the Gospel and to see which ones I thought were the clearest and most consistent with other passages that present the Good News of Jesus Christ and the grace of God freely manifested toward us. In at least one example I preferred the King James Version over the New King James Version: It uses the word “patience” instead of “perseverance.” With its many archaic words, however, and wanting what I recite to be largely understandable for people, I decided to go with the NKJV.
I once read that the word order in NKJV was written to somewhat conform to the KJV such that someone reading the KJV could easily follow along with someone reading the NKJV, and vice versa. Others confirm this. I also read that this approach makes NKJV one of the most unnatural of all Bible translations for reading! That's not at all to say its unreadable, but I can attest that passages like in Romans 9:6-13 may have been more difficult to memorize because of this. Nonetheless, I don't regret my decision. I'm committed to that translation now, and if I had it to do over again, I'm confident the same decision-making process today would lead me to the same decision. The number of verses that took a bit of extra effort to memorize is small compared to the now hundreds of NKJV verses I have committed to memory.
It is also freeing to commit to a translation and trust that it is accurately God's Word. While I have subsequently learned that there are better ways here and there to translate some of the words in the NKJV Bible, for memorization I am relying on the publisher, and many other faithful men of God who have affirmed their work, that the NKJV is true to God and his His Word. If I didn't have that trust, and if I were constantly trying to make my own tweaks to a translation, then who, including myself, could confirm or would have confidence that I have memorized the Scriptures correctly? Sticking to a common translation ensures that one's memorization efforts can also be valuable and edifying for others.