What is the dominant nusach in Eretz Yisrael?

Shalom, Thank you for your question. I'm not certain that anyone has done a census of all those who pray here in order to be able to answer your question exactly. None the less, it would seem to me (based on purely subjective guess work) that the majority of both synagogues, and majority of people who pray, use an Adut Ha'Mizrach (i.e. Sephardi) nusach. However, in many places where there are both Ashkanazim and Sephardim praying together (for example the army, schools, etc), you may find a very widespread use of nusach Sefard – the hassidic nusach that combines parts of the Sephardi nusach with the standard Ashkanazi customs. This is because there are many more people who pray Sefard nusach in Israel than standard Ashkanaz (though I believe, as I wrote above, that overall the Adut Ha'Mizrach (i.e. Sephardi) nusach, is the dominant nusach), and also because it is closer to the Sephardi Adut HA'Mizrach nusach. All this is an interesting social study – but in terms of any halachic ramifications based on this answer (such as what nusach you should use), a specific question should be addressed to your rabbi. I hope this is of help to you, Blessings.