I'm a big fan of affliction. It affords you the following:
1. dots that actually hurt, and are hard to dispell (UA + contagion).. dot up and kite
2. instant fears
3. 20% extra range
4. siphon life
5. curse of exhaustion, and malediction
I played SL/SL on my main in seaosn 3 for a bit, it's nice for the survivability but he hit like a bitch, I have to re-apply dots about 3 times to kill an equally geared 70. and if it's a priest, forget it. they're dispelled almost before I even cast. I feel like a ton of demo locks is just too gimmicky. And for the ones that arent being attacked, their survivability is not being utilized yet their damage is severely gimped. Of course you could just be a one trick pony and put the felguards all on one guy at a time