In this Wikipedia article it is indicated that there are several editions of the Masoretic Text. It seems they are not identical to one another. Is there a standardized text for official use in synagogues? Will we find exactly the same edition in all Rabbinic Judaism synagogues around the world? If so, which edition is it? If not, what are the "acceptable" editions?
Practically, whatever's popular in mass print today for synagogue use. In the United States, figure something printed with an English translation. In Conservative synagogues, it will usually be the Jewish Publication Society translation -- you'd have to research exactly which precise Hebrew text they were using. In Orthodox synagogues, the Soncino Hertz is a bit older, Aryeh Kaplan's Living Torah is certainly acceptable but never became super-popular -- same for the older Koren translation; Artscroll's Stone edition is the 20-ton gorilla that conquered all, and recently Koren released a new one including the late Lord Sacks' translation. Koren is famous for their own research; for the others, you'd have to research precisely which Hebrew they used.
To be fair, as far as what's used by the masses in the 21st Century, we are talking very, very minor differences here. (At least in the first five books, which is what you'd find in mass print in synagogues.) There's a question of literally one silent letter, and even that has increasingly congealed to "A is the right way, footnote -- some texts had B." More of a question of a handful of vowels (e.g. is the mineral jasper yash-peh, yash-feh, yash-fay, or yash-pay?) and cantillation marks, and a few differences on where to split paragraphs. Only people really obsessed about these things will notice/care. (If the cantor gets up and reads yash-feh for "jasper" because that's what's what is in his edition, and someone else had yash-pay, they will compare books for a second, shrug, and move on. A choosy shopper buying a handwritten Scroll of Esther today might be asked -- "do you want the paragraph splits the common way, or consistent with the Aleppo Codex?" It would sound exactly the same when read out loud! Again, the rank and file don't really worry about this.)
Purists will continue to bicker about whether Koren or Breuer reflects the "best" text ... again, very, very minor differences.