That's:
Persona Q
Shin Megami Tensai 4
Shin Megami Tensai 4 Apocalypse
Shin Megami Tensei: Strange Journey Redux
Shin Megami Tensei: Devil Survivor Overclocked
Shin Megami Tensei: Devil Survivor 2
Shin Megami Tensei Summoner: Soul Hackers
Why did I do this? Fuck if I know. Did I make a huge mistake? You tell me. What do I do?
I've never played a single game in this series.
Persona Q is like a crossover between Persona and Etrian Odyssey. If you've ever enjoyed one of those then I bet you enjoy PQ too.
Shin Megami Tensei IV is, well, the fourth numbered SMT game. It's one of two games (the other being SMT4A) in this list to have the series' renowned Press Turn combat system. It has a diabolically brutal first dungeon and then actually gets pretty easy after that. It's a good starting point IF you're willing to bash your head against exactly one wall, early on.
Shin Megami Tensei IV Apocalypse is a quasi-sequel to SMT4. I'd play it afterwards. It has some nice gameplay improvements and far better game balance, but deviates from the original in story/tone. I think the trade-off is more than worth it.
Shin Megami Tensei: Strange Journey Redux is a 3DS re-release of SMT: Strange Journey on the DS. It's not numbered, but its still considered part of the "mainline" SMT series. The original is renowned for being brutally difficult, but the re-release adds some difficulty options (and thus, an easy mode). Aside from PQ, it's the most dungeon-crawler-y of the bunch and has a novel setting/premise compared to the other games.
Shin Megami Tensei: Devil Survivor Overclocked is also a re-release of a DS game. The Devil Survivor games are Tactics RPGs with a SMT twist. If you love Tactics RPGs, maybe these will be a good starting point, but I remember this game also being quite challenging. So, that might affect your decision.
Shin Megami Tensei: Devil Survivor 2 might refer to SMT: DS2 Record Breaker, which is, once more, a 3DS re-release of a DS game. Either way, it's the second Devil Survivor game, but isn't a direct sequel. You can play them in whatever order. I didn't play much of this one, because the story didn't grab me and I don't
love the mechanics of the Devil Survivor games in general. Maybe one day. I can't really comment on this one, but I think its supposed to be the easier of the two games?
Shin Megami Tensei: Devil Summoner: Soul Hackers is a 3DS rerelease of a DS ga-- just kidding! It's a 3DS rerelease of a Sega Saturn game. You can definitely still tell it was originally a Sega Saturn game. If you want some Actual Honest-To-God Old-School Video Gaming, this is easily your best bet. I like it a fair amount, but I'd never recommend it to anyone unless I was
sure they were the sort of person who would be interested in a Sega Saturn JRPG.