I vote Ninja. But if you are personally more interested in AoE focus, that’s when you want to look more at Mental.
Pros of Ninja:
- Sustain may not be a toggle but at least you can put it on auto. Better sustain against hard single targets.
- Comes with a power that is Char but better. If you’re like me and consider Char to be mandatory, this fact opens up build options.
- Better T9 melee power. Accepts all sorts of procs.
Pros of Mental:
- Sustain will be stronger *if* you are paying perfect attention to it and getting Drain Psyches off in larger groups.
- Higher radius PBAoE attack.
All of the other pros/cons are just meaningless distractions compared to these points, IMO.
Since you’re pairing with Storm/ (stronger S/T performance than AoE performance), I could see the case for Mental, but both would be fun.