The teimini pronounciation, which predates the others and is no more similar to sefardic or shkenazic, is closest to the original. Why would anyone think that the sefardic (Jews from Spain and area) pronouciation is closer to the original than the ashkenazic (Jews from Germany and area) is beyond comprehension.
There is no clear timeline when the sefardic and ashkenazic Jews started differing from each other. It is unclear where the Jews of Babylonia went mostly (Germany, Spain, …) after the Talmudic period.