Finally, a thread just for me.
From a general standpoint, IV and V are good places to start. They're the best in terms of mainline mechanics, though story might feel a bit lacking. I adore both with all my heart, but even I'd have to admit the plot is kind of rushed. For Persona, I'd say the 2 duology and maybe 4. I was never the biggest fan of the calendar system, and 5 in particular drags on longer than it should imo.
But from my personal standpoint - I'd recommend Devil Survivor 1 and 2. It's a strategy RPG, and it can be really difficult, especially if you're just starting out. But in terms of writing, plot, character development, overall atmosphere, etc. I feel like it perfectly bridges the gap between SMT and Persona.
Oh, and I can't forget about my namesake! The Raidou duology! They're more akin to an action RPG, and they were a blast to play through. The plot is a perfect mix of lightness and heavyness; it also could act as a nice gateway from Persona into SMT. The music in both games is Meguro's best work imo, also. You can play them in whatever order, but you get extra goodies from transfering your save file from 1 to 2. 1 is admiteddly a bit clunky, but I don't think it's bad. 2 is a huge step up, and a lot of fun.
I could honestly talk about this topic for hours, but I'll spare you from my further yapping lol