Alright so I'm about two weeks into the game so I'm definitely still retarded, but I thought I would mention my thoughts on "safe" investment characters. Which is to say characters you are least likely to regret wasting a good inherit or skill scroll on. I'm posting it partially to help the couple other noobs, but also to give people a chance to tell me I'm wrong or missed something so I can be less retarded.
Fighters
>Abenius
Leveling priest to 30 and then switching back to fighter means that she just has an extra stat contributing to her attack value. Not a crazy game changing one, but enough to give her an edge, which goes farther when you put her with Lana who is one of the best knight options. The free attack once per battle isn't crazy but it is also free damage. Fighters do damage and she has the tools to do more damage, simple as. Gandolfo is worth mentioning here as another fighter-priest who would be the go-to for evil parties, and is certainly easier to Discipline so he can do more damage on more accounts but Heavy Attack is a good inherit so you have to kinda make a decision on your own about him. Not quite the same "safe" pick.
Kinghts
>Lanavaile
>Elise
Really any of the Fighter-Knight characters are worth considering because Knights benefit tremendously from WotW and Counterattack so getting an extra level without pumping 9 copies of a character in provides value. The top 2 stand out because they provide a damage buff and they have defense on their Discipline and especially Lana has good bondmate synergy as a fire type for mates like Albano and Jack.
Thief
>Phillip
>Milana
Phillip has a great passive that is useful in 100% of parties, arranged in any way in 100% of fights, which is rare to say. Milana provides extra damage to evil fighters like Gandolfo if you're using him. Water is good bondmate synergy for dealing with traps, dark for doing DPS, both are valid options.
Priest
Honestly, priests are a hard one. The best one is Alice, who is also the best inherit in the game that you want to give to pretty much any and every character so never putting her in your party is a valid option no matter how many times you pull her, despite her being the best priest. The 2nd best would be Marianne who also has a great inherit. Woof. You kinda just have to follow your feelings on this one.
Mage
>Yekaterina
>Adam
I'd put Yekaterina higher than Adam because I really hate getting ambushed and even though I still get ambushed with her, any reduction is welcome. Adam's unique skill is also chance based though it can work multiple times in a fight and in fights where you had initiative, I don't really consider the damage resist-resistance to be a factor because just learn other spells, but sometimes taking less damage is better than just taking damage. Both also have good inherits, but Adam's is better.