I can't speak for Dark Armor or Spines as I have not played or toyed with them. But I really like Dark Melee. The Smite, Siphon Life, Midnight Grasp combo is fun and I find myself tearing through things with it.
I have a DM/SD which is absolutely love and even at a +3/x8 I burn through the mobs like they are nothing. Jump in and strike the boss with Midnight Grasp and then Siphon Life while Against all Odds builds up (saturates I believe is the term used here). Then hit Soul Drain and Shield charge to take out majority (if not all) the mob. Run your attack chain against the boss once maybe twice more through and it's dead.
Also have a DM/Inv but he is only at level 42 right now. So far I enjoy playing him, get a lot higher resistance than a SD build. I do find it harder to kill mobs at a fast pace without the shield charge though. Survivability is really good though. What damage you do take can be quickly healed with spamming Siphon Life. It is also possible to get a really good (even soft capped) Defenses while keeping a 60-70% Resistance.
I have a spines/da scrapper. She's an AoE beast. In the early levels you might have some end problems but with correct slotting it's nothing that can't be overcome. If you want a scrapper that mows through minions spines/da will get the job done quickly. Not so great at killing bosses but still quite capable.
Edit: she was my first character and she's been though all the tough times; murderous end consumption, exclusive toggles, nerfed CoF, etc. etc. but she's doing well now. I use her to blow off steam on -1x8 farming missions for purples. Mindless, efficient and quite profitable. 
Spines/ D A lvl 50 Scrap, stone/wm lvl 50 tank, Kat/reg lvl 50 Scrap
Grav/Kin lvl 50 Cont, Fire/Enegry lvl 50 Blast
Warshade lvl 50, PB lvl 39, nightwidow lvl 50, crab lvl 42
plant/thorns lvl 50 dom, ice/fire lvl 40 dom, grav/nrg lvl 41 dom
Dark Armor and Dark Melee are great. I dislike Spines, but not for any technical reasons, and Spines/Dark is a classic AoE machine.
"That's because Werner can't do maths." - BunnyAnomaly
"Four hours in, and I was no longer making mistakes, no longer detoggling. I was a machine." - Werner
Videos of Other Stupid Scrapper Tricks
Coming from owning scrappers of the DM/FA and Spines/DA variety, I'll share my observations of the three sets you mentioned.
Dark Melee is a single target focused set (Shadow Maul being the only cone attack) with the primary secondary effect being -To Hit. The majority of its attacks deal negative typed damage (one of the least resisted types in game).
Despite the set being light on AoE attacks , Dark Melee has several utility powers that are worthy of mention.
- Touch of Fear is a single target Fear power capable of terrorizing Lts and below (Mag 3 Fear).
- Siphon Life is next on the list that is an attack and a self heal combined into one power.
- Dark Consumption is an Endurance Recovery power that returns an amount of endurance based on how many foes it hits in range.
- Soul Drain is basically a build up power that provides more +To Hit and +Dmg bonuses for each additional enemy it hits. Midnight Grasp is a ST attack that is also an immobilization power.
Spines is an AoE focused set that has Slow and Toxic DoTs as its secondary effect (along with some long animations
). Its worth noting that this set is the only Scrapper Primary with a damage aura(Quills) and has two short ranged attacks: Impale (ST ranged) and Throw Spines (Targeted/Ranged AoE). You can also customize the spines to look like something else besides bananas shooting out of your body. Some good synergies are with Dark Armor, Electric Armor, and Fiery Aura. The rationale is that these sets provide an additional damage aura. Please note Spines cannot be paired with Shields.Dark Armor is a resistance based set (very high in Psi and Negative resistance) with access to two crowd control auras (Oppressive Gloom is a stun aura, Cloak of Fear is a fear aura) in addition to its damage aura (Death Shroud). It also boasts a stealth power (Cloak of Darkness) as well as a self heal (Dark Regeneration). Dark Regen. is often touted as the best heal in the game, but this comes at a high endurance cost per use. The high cost to heal in addition to the dependency on several toggles to survive is what gives this set a bad rap (Recovery can be slotted for using IOs to mitigate this sets end hoggishness). Dark Armor does not offer any native resistance to knockback like other scrapper secondaries do. Some notable combinations besides Spines and Dark Melee (both synergize well) include: Katana(or Broadsword)/DA (Werner has demonstrated that this combination can soft cap to nearly everything), Martial Arts (Stack-able Stuns with DA's Stun Aura) and possibly Claws (its very endurance light)
I hope this provides some insight on these sets (and that I didn't miss anything critical)
Good Luck on your next scrapper!
Thank you very much everyone for your great replies. I was always curious about these sets, especially DA, so I think I might have to go try one out!
Hey everyone I just had a some quick questions about a couple of powersets that I haven't tried before, but are interested in. I was curious how Dark Armor, Dark Melee, and Spines are. Not necessarily together, but what other choices work well with them/or what I should stay away from.