It depends on the scenario. For single target hunt objectives I like smn because it is just bio2, miasma, bio, fester -> dead. If you have Raging Strikes from arc it is even better. And combining Spur (lvl 45) and Enkindle (lvl 50) also does a good chunk of aoe damage.

Since you are still leveling though and haven't even faced Titan or Garuda there is going to be a lot of work involved with summoner. Certainly until you fight Titan just use sch. If, after Titan, you feel like you need tank help for soloing then you can try smn. Before then sch + cleric stance is your best bet.

BUT you should get thm up to 26 for swiftcast no matter which route you go.