Or, a skill that favors a sneak build more then any other playstyle?

Personally, yeah. The game balance for Illusion renders all of the Fury/Calm/Fear spells completely pointless after like...LV5. Sure you can dual-cast, but then you have to dual-cast, hope and pray that it works, and switch to actual weapons or spells before you get an axe in your head.

To make things worse, Master of the Mind is a really late perk and the game is positively filled with undead enemies immune to Illusion spells. It's just such an impractical tree for anything not Muffle or Invisibility...

Frenzy is definitely most effective with sneak. But fear and calm are great when not sneaking too. I have a non-sneak illusion/conjuration mage that uses a lot of fear spells.

My druid uses it to buff his companion
Sooooo... He doesnt use it in a stealthy manner.

Also, fear is good for crowd control (not stealthy) and calm works well to give you a free sneak atack on the last enemy of a mob (kind of stealthy I guess)