my archer is pretty low so i may not be right, but i think that since the archer's main job in a party is damage dealing, i think 25 spr and full str is best, and that archer's dex is already high enough...
Because Archers have a naturally high DEX stat you can opt to further improve their assets and add to that stat (but don't bother past 50) then go full STR. If you plan on becoming a long term player it isn't a bad idea to add in DEX.