>>719838639 (OP)
I think the 2 duology is massively overrated on here, it used to be talked about a lot more a couple years back, showed up in a lot of 3x3 threads etc but I hardly see it anymore.
I didn't like Innocent Sin much, but you should still play it before Eternal Punishment, which I liked quite a bit more.
Both of them are hard sequels to Persona 1 with returning party members and plot threads, that being said you can still skip it, but I think Persona 1 is worth a play anyway.
Realistically if you've never played a Persona you should just play 3, 4 or 5, the 2 trilogies are basically 2 different series that just share a name. You won't get the experience that everyone thinks of when they hear 'Persona' from 1 or 2 duology. You can always return to it later