@minokins
For Boxer, if you plan to be diverse, you should have 22 DEX at most. The slowest gloves only need 22 DEX to go at their fastest speed, 5-10 AGI. If you plan to be a magical boxer, you should probably invest 100 SP into MAG and the remainder into STR. If you don't care about magic, just do all STR after DEX.
Gladiator is, uh, special. Again, whether or not you want to be magical is up to you.
Whipper's magic is far better than his physical damage, so it'd recommended to specialize in DEX and MAG for him. I'd personally say 80 MAG, but it's a touchy balance between it and DEX.
For Angel, I find that you should never get all 5 rings total from DEX. 60 DEX, which gets you 4 rings total, is the most the Angel can fire at the same time for normal rings. The rest of the SP should be spent into at least 75 MAG, and from there STR.
Priest is meant to be a support, so unless he's your last resort, you typically want to give him lots of colored stones to enhance his aura's powers. Don't spend any SP into MAG, as that only increases range. Of course, if your team is supposed to be distant, then you might want to give him a long-ranged staff or a little bit of MAG.
For Gunner, spend some MAG in the beginning so you don't go completely broke. By the time you get to the Forget Tree, if you think you have enough money to use guns at their full costs, reset your SP so they're purely STR and DEX. Don't spend too much in DEX, as getting to 5-10 AGI on all guns requires tons of DEX (it's a root decline).
For Sniper, have at least 40 MAG (for some magic bows) and don't spend anything in STR (unless, again, you're meant to be distant from enemies).
For Magician, don't spend anything in STR unless you want distance on purpose.
That's about it. Look around the wiki a bit to find what weapons you'd like to use if you want to specialize your characters in using specific weapons.