While many issues must be considered to adequately cover the subject of translations, perhaps the most basic issue boils down to whether translators consider the Byzantine or Alexandrian texts to be the most reliable. Good arguments can be made for both sides.
The Alexandrian manuscripts, used by most modern-day translations, are the oldest; therefore, they are believed by most modern translators to be more reliable. This argument is based on the fact that these manuscripts have been copied less.
Before the advent of the printing press, the Bible was copied by hand. Although scribes were most meticulous in their work, they were still human and prone to make mistakes, especially when greatly fatigued or working in dimly lit scriptoriums. Thus, the older manuscripts, having been copied less, are believed by most modern translators to be less likely to contain human error.