Old Testament in First Century

Both were in regular use. The Hellenistic Jews would have been those most likely to use Greek translations, but there really wasn't a single identifiable "Septuagint." The Greek translations were largely local translations, or portions of translations gathered from other regions. The Septuagint took a long time to develop. People in many areas were making multiple translations of the Old Testament in Greek over a period of perhaps centuries. There was no single unified or accepted Greek text in use at the time the New Testament was written.

It is also worth noting that the Greek translations were not always made from Hebrew texts which parallel our modern Hebrew texts (i.e. the Masoretic Text). Sometimes, the Greek text translates a Hebrew text that is not represented in the Masoretic Text. The Dead Sea Scrolls have demonstrated that some documentary lines that existed in the first century are not represented in later documents. For example, the Dead Sea Scrolls have two different versions of Jeremiah, one of which is much longer than the other. Among other things, this indicates that Jesus and the apostles had similar textual problems to those we encounter. The nice thing for us is that it didn't seem to bother them. They did not place the same emphasis on letter-for-letter preservation that many modern Christians do. Nevertheless, they believed the texts they had were accurate and authoritative, even though they were not identical.