I would read up on how 4 has more of like an overworld that you're traversing with an airship to visit many different dungeons. If you find that idea appealing, I would go for 4. But if you prefer the crawl through a single giant dungeon then its either 3 or 5 I think. 4 is also the one I remember being the most puzzle-y which was another big component of why it is my favorite so far.
I would tend to agree with this. The fourth entry, in all honesty, is probably the best balanced of the series. That's not to say there isn't lots of OP stuff, but rather than it being limited to a few classes, pretty much every class is equally good and capable of their own ridiculous combo and can actually compliment the ridiculous combo of another class at the same time.
I also find the pacing to be supremely on point, with the mini-dungeons and shorter, but more considerably main dungeons to really help keep things fresh throughout the game. The overworld is a dungeon all its own and works well to compliment the rest of the game, actually giving the entire thing a semi-Metroidvania vibe. Rather than just locking things away until you have X key, you continually improve your ship, gain additional items, and proceed through events which unlocks more and more of the pre-existing overworld for you to go back through. Then when you reach the end, you get taken on what amounts to a best of the best tour of everything you've done up to that point and when you realize what's going on, it's very satisfying to get through.
And then you reach the sixth stratum and get ambushed by a lion, a ghost, and a pile of electric goo. Dammit.
