most people go with robes and acumen weapon, so they can heal their pet.
Personaly I did use Plated leather set and sls/focus in C.
aoba/health and BW LA in B. I would use a bloody orchid/focus and still use my BW LA in A. Im not much of an caster, I like to DD along with my summon.
Every summoner has it's own playstyle and the gear you use should mostly depend on what you kill. I personally like pink mobs for exp with my warlock, and for that you need something that can actually connect hits, so sls/focus was my choice.
Armour depends on how much healing you have to do and how much aggro your pet generates (the higher the level the more your damage becomes relatively puny so the more you go with fast cast robes). At 48 you'll be the tank so light armour is good. Between 52 and 60 your pet will start hitting enough to steal the aggro within a few hits.
Some summoners also go in nuker mode for 40-48 in which case they either go karmian + acumen weap or a combo with more m.atk depending what they kill and how many + they can afford on sword.