Depends on your build and what your character needs.
Minions mostly scale with +CA stuff, so most of the time you go with +CA or +skill (to raise AL Focus and avoid penalties) rings/neck/runes.
Alternatives include the blacksmith arts: Enhance (for those who rely on AL CAs and need to keep regeneration times manageable, I prefer this), Anneal (for those who need more survivability for whatever reason), and Whet (for hybrid warrior/summoning SWs).
Edit:
BTW, I'm honestly not sure why people would pick Scatter Shot over Perforate, especially on a dedicated summoner. The problem with being a dedicated summoner SW is that you need crowd control/a great Area of Effect damage combat art, especially if you like fighting large groups of enemies at once (which you should be, imo).
Perforate very easily outperforms Scatter Shot in my games because of this. Contrary to what people are saying/what is written in the Sacred2wiki the projectiles from Skeletal Fortification actually have a decent-sized hitbox, and as long as you position your fortifications tactically they should have no problem hitting 2+ mobs per attack. This is very easy to test - get Perforate on a newbie SW, aggro as many monsters as you safely can, get them to cluster around you/your minions or just kite them so they form 1 big group, drop Skeletal Fortification, watch as each attack generates a dozen damage floaters. It's like spamming the Necromancer's Bone Spear spell from Diablo 2 except much, much more convenient.