The Chida writes in the name of the Ari that the Sephardic nusach ascends through all twelve gates. Therefore, in his opinion, Ashkenazim are permitted to switch to the Sephardic wording of prayer (see Yabia Omer 6:10; Yechaveh Da’at 3:6). However, the Chassidim claim that their nusach (Nusach Sephard-Chassidi) is of higher quality. They maintain that the prominent Chassidic authorities investigated numerous wordings and formulas of the Kabbalah, and selected the best among them. Those who pray in Nusach Ashkenaz assert that their custom is the most meticulous, for it was passed on from person to person as far back as Shimon HaPakuli. Furthermore, the foundation for the Sephardic minhag lies within the Amora’im and Geonim of Babylon, whereas the basis for the Ashkenazic minhag originates with the Amora’im and Geonim of Eretz Yisrael who were more proficient in Agadah, Chochmat HaSod, and nusachim of prayer. (Incidentally, that is the reason for the similarities between Nusach Ashkenaz and the original Yemenite nusach [Baladi], for both were influenced by the Geonim of Eretz Yisrael.) The Yemenites, too, claim that their nusach is more precise, for the Jews of Yemen, in all their years of exile, did not wander. Instead, in response to the persecution that the Arabs inflicted, the Yemenite Jews intensified their devotion to Torah and observed their customs with extra stringency. Indeed the Yemenite Torah scrolls were found to be closer in accuracy to the nusach of the precise Keter Aram Tzova.
In summary, every minhag possesses its own advantages and it is not in our power to determine which minhag is more praiseworthy. As the Chatam Sofer writes (responsa 1:15), all nusachim are equal. He maintains that the Ari composed his kavanot for Nusach Sephard-Chassidi because he was accustomed to praying in that nusach. However, if a person like the Ari were to have resided in Ashkenaz, he would have written his kavanot based on Nusach Ashkenaz.
Even if we were to know that a particular minhag is more precise, it would still be proper for each person to continue his own minhag, for even the less accurate minhag surely possesses advantages that the others do not exhibit. Only after the Sanhedrin is re-established will we be able to institute a uniform nusach, which will include the benefits of each minhag. Though, even then, there will be room for different emphases in the additional prayers and varying melodies, corresponding to the twelve gates; each community according to its ways.