Stormcast are great.
IMO from a competitive point of view there is no reason not to take as many as you can because they are SO strong.
From the top of my head:
- Knight Venator is a flying sniper with huge range and enormous damage potential
- Gryph Hounds can protect you from deep strikes and they are cheap.
- Celestant Prime (now only 320 points it seems) can dish out multiple mortal wounds (without even rolling a dice) at 24" and isn't easy to kill.
- Lord Relictor can do something similar (and more) and is cheaper.
- Protectors help against shooting if placed in front of our units
- ....almost everything else by SCE. Just switch over and play their army, no need to play any Seraphon. Yes, they are THAT strong.