There are no very good translations of the Dead Sea Scrolls (DSS) in to English (avoid anything with Geza Vermes’ name on it especially). There are several serviceable-to-good Septuagint (LXX) translations. From what I’ve seen of the Eastern Orthodox Bible - the New Testament, which has been out for a while - I would not trust the translators to get Genesis 1:1 right, which is understandable, granted that it’s being translated, edited, etc. in a Wikipedia-like fashion mostly by people who have very little understanding of the original. The Holy Apostles’ Convent New Testament (in 2 vol.) is better if you want an “Orthodox” edition, but it’s very, very wooden (I’m not talking NASB-level woodenness; I’m speaking of Concordant or Young’s Literal-level), and constantly mistranslates any words with the root “erg” (energy or work words) to reflect the essence-energies distinction, like the NIV mistranslates “paradosis” (tradition) and sometimes the “erg” words (with a focus on cheap grace as opposed to grace working through faith/Lordship Salvation).
The Orthodox Study Bible’s OT isn’t even an LXX. It’s called an LXX (the “St Athanasius Academy Septuagint”), but there are more places where it contradicts the LXX and agrees with the Hebrew than vice-versa. It’s, as known, an NKJV OT and NT (which is an excellent translation), but with the OT once-overed to get some of it to agree with the LXX (basically, the numbers in the genealogies, granted that the story of Cain and Abel is likewise from the Hebrew and is missing the LXX “let us go abroad in to the field” addition). It may be usable for devotional reading, but for study of the Septuagint, no.
Now, to the actual English translations:
You have Brenton, which is a Greek and English diaglott, almost an exact reproduction of Vaticanus graecus 1209/Codex B, instead of a critical text. Some, but few, variant readings from Alexandrinus and Sinaiticus are listed in the margin. It uses the King James Version as boilerplate, and conforms it (properly and fully) to the LXX, so it uses archaic English. I recommend this version for those who have some facility with Greek. It translates the standard Hebrew canon, and puts all of the LXX extra material (which became the deuterocanon) in the back.
You have the New English Translation of the Septuagint, which is English-only, and is based on the thoroughly modern LXX critical text as distilled from both the Gottingen Septuagint and Rahlf’s. It uses the NRSV as boilerplate, and conforms it (somewhat less properly and fully) to the LXX, so it uses modern English that is sometimes gender-neutered and often has the prophecies of Christ or foreshadowings of the Trinity removed (such as Gen 1:2f), although not as badly as the NRSV. It has the Hebrew and Greek books interspersed in ancient LXX order, and translates several versions of some books, such as Kings and the Prophet Daniel, which are extant in multiple ancient Greek translations. I recommend this version to people who already use the NRSV (since it allows for easy comparison of the LXX and Masoretic text), and for those who have no knowledge of Greek whatsoever.
Then you have Rahlf’s Manual Edition, which is Greek-only, and is my recommendation for those who can read LXX Greek.
Avoid the Panayiotis Septuagint for any use (it’s plain wrong), and the OSB Septuagint for any “scholarly” or “studied” use (involving comparison, etc.) as opposed to a quick reading.
For the Dead Sea Scrolls, I would avoid anything with Geza Vermes’ name on it, as I mentioned. He’s like the Jewish version of the Jesus Seminar, and is involved with many DSS projects, and is the editor/commentator for all of the Penguin editions. For the DSS, the best and foremost authority for English translation is Martin Abegg, director of the Dead Sea Scrolls Institute. I would recommend The Dead Sea Scrolls: A New Translation. Translated and with Commentary by Abegg, Wise, and Cook. The translation called The Dead Sea Scrolls Bible by Abegg, Flint, and Ulrich, which is a less-detailed and more-popular (sensationalist) presentation of the material in A New Translation, lacking most of the commentary and having ellipses and lacunae filled in by the editors instead of being left blank.