dont know very much about MA, but got a lvl 30 scrapper with dark armour, so here's what id suggest from that.
DEATH SHROUD slotted up with a few damage and accuracy with an end red is very useful when taking on mobs of more than 2 people, and if ya can spare the end run it as much as possible.
OBSIDIAN SHIELD is a must so u have resistace to hold, sleep etc etc. scrapper without that is asking for debt.
DARK REGENERATION is a great heal but does depend on .
hitting so its needs at least one accuracy enhance in it
also very inportant for dark armour is getting fighting power pool to get tough and weave to boost your defense, otherwise can be a bit squishy.
i would also recomend getting super jump power pool as acrobatics is very helpful because it provides knockback protection which is very important for scrapper class
other than those i would say all the powers are optional and usefulness will vary according to play style etc
however these are just opinions from my experience with the first 30lvls with dark armour and i could be totally wrong 
MA/DA should be a really nice build, prolly hard in the early levels like most DA but get really nice later, because your MA and more single target i'd leave out death shroud no need for the PbAoE damage.
For shields i'd suggest
Dark Embrace : 3 damage resist 2 endurance redux
Murky CLoud: 3 damage res 2 endurance redux
Obsidian Shield 3 damage res and 2 endurance redux
Cloak of darkness 2 endurance redux (this'll serve you well in PvP because of the +perception, the immobilize protection, although if you want the cheaper endurance option combat jumping will serve you well in PvE)
Power pools you'll probably want to consider is leaping (for acrobatics, no knockback resistance with DA and combat jumping will give you immobilze protection until cloak of darkness) fitness,fighting and possibly speed pool if you want your attacks to cycle better.
I'd advise taking tough now due to ED and loss in s/l damage res.
Furthermore oppresive gloom will be nice with your MA for multiple stun control on mobs, allowing you to stun lts and boss's with cobra strike, and the minions will be out of the fight.
For dark regen, its very endurance heavy so 2 accuracy and 3 endurance redux works well, the base recharge is nice, if you have slots to spare stick a recharge reduction on it.
Any spare slots you have left I'd stick on the shields. DA will be very toggle heavy, which is a major downfall.
Thanks, that's exactly the sort of advice I wanted 
Don't know about DA but for MA get Cobra Strike - if they are stunned they can't hit you back.
UNION @Flitz 50, Lead Hose 50, Red Rag 50
DEFIANT Rose Bloodthorn 34
VIGILANCE Captain Caledonia 20 - Yeah, I made toons on the French server coz we only had 4 back then (might have to transfer/recreate them on one of the US servers)
..and many more!
Any that anyone can give me? What's good? What's optional? What should be chucked in the nearest bin?