As you correctly pointed out, if a Catholic attends the vigil Mass, it does fulfill the Sunday Mass obligation. Since you aren’t Catholic (yet,) you’re obviously under no obligation to go to either. Still, the Sunday Mass would be an additional experience for you to take in. The readings are somewhat different in both the Ordinary Form (English) and Extraordinary Form (Latin Tridentine) Masses. The Vigil Mass, especially if there are baptisms, first Eucharists, and Confirmations going on, is considerably longer, so if you are bringing young children, or have difficulty when sitting for a long time, that might be a consideration to take into account.
Whichever you decide, or if you do go to both, Happy Easter!