Dark has a better heal and some interesting options with fear and stun auras. Dark uses A LOT of endurance.
Electric has better resists and actually helps with endurance.
I don't have a spines/dark, but that's a very common build that a lot of people play so there's a lot of discussion about it on the forums. I do have a spines/elec and I enjoy it a lot.
I gotta make pain. I gotta make things right. I gotta stop what's comin'. 'Least I gotta try.
I went with spines/elec, and I definitely appreciate power sink - no worrying about endurance.
I would suggest Elec as it is one of the best all round secondaries. Good heal, nice resists, damage aura and no end problems after 35. 
@Fail (Used to be @Tux) and @Tuxedo Infinitus Defiant/Freedom/Champion
Favourite Toons: Prosper [Ill/Rad] Controller :: Infinitus [Fire/Elec] Blaster :: Pocket Dynamo [Fire/Shield] Scr :: Fast [Cold/Sonic] Def ::
Inspire [Plant/Storm] Controller :: Quality - SS/Fire Brute :: Double Down [DP/Kin] Corr :: Pwnz [Fire/Cold] Corr :: Fail [Fire/Son] Corr
I'm playing up a spines/elec at the moment and it's really fun. I like the idea of having capped energy resistance, tons of S/L with Tough going, and infininte endurance with Power Sink/Energize. The heal is ok and if you're not afraid of inspirations you've got a very sturdy build that has tons of damage and two damage auras to melt everything around you. Grab Fireball from your Epic and you're golden. Pick fights against enemies that are heavy on the S/L/E damage, like Rikti, and you can steamroll very effectively.
I just hit 21 and it's starting to take off now. It was kind of a slog getting there, though. Crap ST damage and endurance woes can slow you down. Like most scrapper sets, once you hit SO range it'll start to come into it's own.
You can't go wrong with dark or Elec, i have spines/elec at 50 and he was a blast getting there (once you get so's) great damage aruas and end management, dark has your stuns and cloak of fear (which is cool,i love seeing my enemys tremble) no kb protection but you can slot kb io's and a nice heal,but if i was just to pick 1 though id go for elec . Johnny
Johnnycash-''Morning bright eyes!!''
Mrs johnnycash-''P*****F im sleeping''
I have been wanting to make a spiner for a while. The debate I am having is what secondary to take.
It seems that the best defense is between Invul, Dark Armor, or Electric Armor. I am trying to avoid Invul because I have it on my tank and want something different.
Dark Armor (without IO sets) gives def against everything except knockback. Electric armor seems to give more def and can easily hit the cap vs. Energy, but no Toxic def. It also has KB def, but uses more end to keep the shields up.
I will be teaming mostly with this toon, but solo occasionaly. What secondary is gonna allow me to survive the aggro of the AoE king best? End has to be a major issue. Maybe I would be better off with regen or Invul?
Thanks for any suggestions...