The Septuagint (LXX) is the Tanakh translated from Hebrew to Greek about 250 years before Yeshua. It was almost certainly the bible of the synagogues in the world in the first century.
The Masoretic Text is the Hebrew Bible and dates to about 900 AD. It's the source for the Old Testament for almost every printed English bible in existence.

BOTH of these sources are very valuable for study and they agree with each other almost all the time. If folks are trying to make you pick one of these over the other, you need to not listen to them. That's a false choice. Put in the work and study to show yourself approved.