Take OwtS if your build is running global defense bonuses at the sfot cap or if you lack the endurance recovery to sustain Darkest Night for extended periods.
Take Darkest Night if you are not at the soft cap.
Personally, I suggest Darkest Night. A decrease in the enemies to hit and damage is ALWAYS good. Plus the sets that can be slotted into it have some decent bonuses.
It will make keeping aggro significantly easier too.
If you team a lot Darkest night is your best bet. Not only is it personal mitigation the debuffs help the whole team.
Also remember that OwtS is pretty good without any slotting, but DN will need some slots to be most effective.
Level 50s: to many to remember at this point
Darkest Night is also really useful for soloing at high numbers like +2/x8 if that's your bag. Darkest Night the furthest one away and it'll pull the entire group in a nice clump so you can corner-pull, Soul Drain and go to town with Dark Obliteration and Shield Charge. Best part will be they won't be able to touch you. Basically if you plan on doing anything but soloing AVs (and even then DN has its uses, but less so as it's a real blue bar destroyer), then DN is your best bet.
I working on a build for a DM/SD brute, and as it stands right now I only have room for one of these two powers.
Which one do you think is better - the -to hit and -dam from Darkest Night on nearby foes, or the +hp, +Res, +Rec on "One With the Shield" - given the End loss when it ends. (I'm not counting the status protection bonuses, as they will rarely be a factor due to Active Defense)
Thanks for any input.