Actually Sabin's Blitzes do use the Magic stat so you may not want to neglect it. Edgar Vigor and Strength affect his tools so go that route but better for Edgar is actually giving him the Dragoon relics cause the game fails to mention that Spear weapons (which only Edgar and Mog can equip innately) do 2X damage with the Jump command.

Setzer's Slots use Magic stat but later in the game you can acquire his ultimate weapon the Fixed Dice which perform random damage that is "fixed" towards your benefit. Even better is that its algorithm ignores the balancing algorithm that the Offering Relic uses. The Offering allows you to attack 4 times in a row with an equipped weapon, 8 times if you are using the Genji glove but the weapon halves the damage of the weapons so in the end you are doing something close to 2.5x the damage as opposed to 4x damage as you would think. There are several weapons that ignore this property and do full damage per blow, Fixed Dice, Valiant Knife, Atma Weapon and I believe the Ragnarok and Illumina weapons as well though I could be wrong on those two.

Terra and Celes are good with Magic but they also are some of the few characters that can equip the best weapons in the game. They pretty much have the best options overall but technically Terra is debatably better than Celes cause her Magic stat is higher and the end game weapons compensate for Celes have slightly better strength, not to mention Morph makes Terra damn near indestructible by end game. Runic's usefulness is situational since you are now reaching the point where your party gets access to all the really good magic so Runic will be a bane in any party that has a dedicated mage.

Basically I would go this route. Be sure to note that raising HP and Speed should always be in there somewhere. Stamina is useless so don't bother.

Terra - Any (I usually gear her towards a mage)
Locke - Speed and Strength
Celes - Any (I usually gear her towards a fighter)
Edgar - Strength
Sabin - Magic and Strength
Cyan - Strength and Speed
Gau - Any (He's got funky algorithms that make him broken)
Shadow - Strength and speed (Magic if you want his Skeens to do more damage)
Setzer - Magic and Speed
Relm - Magic and HP
Strago - Magic and HP

If you are going for really good stats you should try to keep your levels low until you acquire most of the Espers.