Mo secondary is the best, but that does NOT mean you should not play with other options.
For instance, you can take /W and use WatchYourself + Protector Strike (doesnt matter u have no strenght) + Mystic Sweep + Eremites + Zealous Vow [E]. It's fun in some PvE areas for some frantic action

(seriously, you're pressing the buttons as fast as you can!)
If you just want simply the best, then try out my Juggernaut build (it's posted somewhere in the forum but im too lazy to find the link):
D/Mo Juggernaut
8 prot prayers
15 mysticism
the rest in scythe
(scythe with 20% enchant mod)
Reversal of Fortune
Protective Spirit
Crippling Sweep
Chilling Victory
Heart of Fury
Avatar of Dwayna [E]
Mending Touch
Rez
I suggest you try it out just for the feeling of it. There r a few game missions where i personally wont use it (those artifically anti-enchant game areas), but other than that it's fun and cool. Keep prot spirit on urself and spam RoF like mad when ur attacked. RoF is FREE on 15 mysticism. Yes that's right, 165hp heal every 2 sec, and since RoF is 1/4 cast time you can keep attacking as well. Dont worry you're not a "tank", your damage is big in PvE, bigger than the dmg warrior one, and your tanking is better as well.
But my suggestion would be to find the build which suits your playstyle. Besides, playing one build will get boring. I also like D/A Lyssa w daggers in RA, but i dont think that would work in PvE since scythe AoE is much stronger there.