Shizuku (Healer + dps boost, she broke the game prior to her nerf but is still massive, aka umbrella girl)
Christina ( Blue hair mage, probably ur strongest if not friendly mage starters, not the strongest late game but will carry u through contents u need to clear as a starter to get stronger.)
Mei (Ur go to dps pvp and pve physical dpser, she will always hit charcter with highest atk power, beware of high end pvp where pple adjust atk power. Loli orange hair gun girl)
QianCao (Single target magical dps, Did i hear u need someone to kill guild bosses and bosses who arent strong against magic in 1 attack? Warrior Cat? Dog? black hair twin swords)
Risa (Simple, easy, low end requirement power battery, if paired with Shizuku and spec'd atk correctly to not take umbrella's buff (or can), can make ur dps just.... obliterate. Mystic, Palewhite? hair girl with beret)
Tanks: Anyone, (most will start with Hotaru since she provides mag def buff for team when farming the end game gears. Purplish hair sword girl, Tank) From there some go to the tank u get at 2-1 for more dps boost or Benimaru(orange red fire-y hair tank girl) if u want PvP tank.
Gear stats u want:
Dps: Atk > Crit > Atk Spd/Crit Dmg >Crit Dmg/Atk Spd
Healer: Atk Spd > Block Chance > Atk (For Shizuku specifically: Atk just below enough ur dps to get her own buff but not the #1 highest dps to get other party's buff, atk spd, block chance)
Tanks: Block Chance, Atk Spd, Atk, Crit/HP/Def/ M Def
Mystics: Atk spd, block chance, atk, crit
Runes, honestly everyone runs all atk% runes on weapons unless u need to adjust atk values then u equip crit/crit dmg/ block if anything.
Rune on Mag Def equipment is usually Hp heal per attack for Dps/Tank or if u are seeing ur team not getting 1 shotted and dying alot. Majority of others wear Mp regen per hit for cycle consistancy and mana burns if any from bosses.