I’ve been wondering for a long time about the correct accent to use when speaking hebrew and leining etc. on the on hand Ashkenaz differentiates between Patach and Kamatz etc. which would appear to be better but then I heard the Sephardi is better because there are contraditions in certain songs with the Ashkenaz one and Sephardi is used as speaking Hebrew in Israel and its more authentic....so which one is the best or most correct? I know this isn’t the most important aspect about davening etc. but I learnt that the Vilna Gaon was very particular about speaking properly and correctly and I feel that it would help me and that it is important to me to be able to speak in the best way possible.

The Poskim can't reach an agreement on what is the best and most correct pronunciation (it seems the Yemenite Jews have the most accurate version), all however agree that one should not change his family tradition. (See Igrot Moshe OC 3 5, Yabia Omer 6 11, Heichal Yitzchak OC 3) One should also note that an attempt to change a long practiced pronunciation may cause a Kavanah distraction which by all means is more important than the pronunciation itself.