Im about to hit B grade on my elemental summoner and i dont know whether i should stay with robes or go with light armor. What light armor should i get and what weapon should i use??
Try looking at http://www.l2pets.com.
Most summoners go BW light for b grade because you get the protection of light armor, with the casting speed of robes.
With weapons, dual B grade swords or focus dagger + shield are likely melee options. If you're still using level 35 nukes or want the best out of your servitor heals, a high m.atk weapon with acumen + shield are best.