“When it comes to halacha, when two of the three, Rif, Rambam and Rosh agree, Rav Yosef Karo, the mechaber of the Shulchan Aruch, paskens like them. The Rosh escaped to Spain, so the sefardim accept him also.”
According to Rav Ovadia Yosef in his intro to his comments onof Halichoy Plan on the Ben Ish Chai, the reason why Rav Yosef Caro chose those 3 is because they rendered halachic psak, whereas other commentaries on Shas were no necessarily deciding ha