The Watchtower accepts the accuracy of the most ancient Christian Greek manuscripts that exist, which they believe are God-breathed. All except for 237 instances where in those ancient manuscript include the word Kyrios (Lord) is found.
The NWT footnotes tell us the sources of their preferred translation to justify these 237 alterations. These are relatively modern translations into Hebrew, by Trinitarians mongst others, between 14th and 20th centuries. But some they are translations from those ancient Greek manuscripts that just do not contain the Divine name. The tetragrammaton simply does not exist in any of the 5,000 extant ancient Christian Greek manuscripts.
Did the WTS really consider modern Hebrew translations, translated with the Tetragrammaton systematically inserted into them for no other purpose than to prove Jesus is God, are more reliable than the ancient manuscripts they were translated from? There preference for modern translations from Greek to Hebrew elevates those modern translations above the otherwise "inspired" ancient manuscripts. But they only select one word "Jehovah" from these versions and would not touch the rest with a barge pole.
For this reason, the least trusted New Testament for me is the NWT, although the Kingdom Interlinear Greek & English shown alngside the NWT wording appears sound. Likewise, the Hebrew OT appears sound. I just wish someone would put together the best versions of Old and New Testamants in one book, without the added falsehoods.
The only thing putting me off the New Jerusalem Bible is that JW stalwarts are recommending it!? I'll read up on it though.