So got my first level 30 class quest

[Darkstride]

yesterday! used the stone to become summoner. This is lets say my first ever class to make it to 30. How differnt is it from being an arcanest?

It's better. There's no real advantage to using Arcanist once you've attained Summoner.

Summoner gets:
Stronger pets
Stat boost
Summoner abilities
-Fester: high damage
-Painflare: high Aoe damage
-Dreadwyrm Trance: damage buff
-Tri-Disaster: instantly applies all 3 DoTs
-Deathflare: massive damage
etc, etc

At level 30 there isn't a major difference but as you begin to acquire Summoner abilities, you'll start to feel how much more powerful it is.