I, maybe compulsively, like to try and keep everyone around the same level, you're only as strong as your weakest link. This causes problems with strategy RPGs where you have dozens of characters. In Fire Emblem 3 Houses most of my units were like 8 levels below the recommended level because I didn't concentrate the exp. But I had still managed to beat it and had a fun time, with that extra level of challenge.
When levelling up I like to cover my weaknesses. A point in something you're weak at is more important than in something you're good at. 2 -> 3 magic is a bigger jump percentage wise than 12 -> 15 strength.
For SMT 5 in particular I put most of my points into magic, a healthy amount into vitality and some into agility. If I was doing well I would increase offense with magic. If I had died recently or the enemies were doing a lot of damage, I would spend some points in vitality.