3, 4, and 5 are all great in their own ways. I loathe 4 but its beloved by many.

I will always recommend 3 first, because the QoL changes after make it impossible and frustrating to go back to. But many of the frustrating elements are part of the experience (no control over party members gives them more personality, fatigue makes dungeon crawling much more time sensitive rather than endless grinding, etc.) and are well worth experiencing because of the amazing style and story.

Its also the last one to be more Old School RPG, compared to the newer two's Social Life Sim RPG. It still has all the same elements, but it feels like like escapist wish fulfillment (people don't worship you, you can easily ruin friendships forever, you need to actually know these people to progress). And has some of that brutal difficult Atlus is famous for, that was toned down considerably for the more mainstream 4 and 5.

Basically, play 3 its great. 4 is the most "weeb slice of life" and if that didn't appeal to you already it'll turn you off massively. And I'd say play Persona 3 FES as the primary version, as it was the re-release that didn't cut most of the game and nerf the difficulty like Persona 3 Portable did. Vanilla Persona 3 has no advantages over FES.