Which is better when the time for 'Isha prayer begins: performing the confirmed post-Maghrib Sunnah or the unconfirmed pre-'Isha Sunnah, if the Maghrib Sunnah has not been prayed?

If the time for 'Isha' has begun and you have not prayed the ba'diyah (post-Maghrib) Sunnah of Maghrib, it is legislated to make it up at any time. If the time before the iqamah (call to commence prayer) for 'Isha' is sufficient to make up the Sunnah of Maghrib and perform the qabliyah (pre-Isha') Sunnah of 'Isha', then do so. If it is sufficient for only one of them, then prioritize the qabliyah Sunnah of 'Isha' and make up the Sunnah of Maghrib after the 'Isha' prayer. However, if you do not intend to make up the Sunnah of Maghrib later, then pray it before the obligatory 'Isha' prayer, even if the qabliyah Sunnah of 'Isha' is missed, because the Sunnah of Maghrib is more emphasized.