Quell the debate!

I think this is pretty much correct. I have an IO'ed fire/shield/blaze scrapper and an electric/shield/mu brute. While my scrapper does better than my brute, it's largely because I have more invested in her and possibly due to the fact that shield charge for scrappers is so strong.

I'll have to concede that for pure farming purposes, a heavily IO'ed electric/shield scrapper is probably better than my fire/shield. However, fire/shield isn't a slouch in that department by any means, and the build is more flexible since it also has a strong single target chain.

Survivability wise, the electric/shield wins out a little bit too since lightning rod and thunderstrike also knockdown mobs, providing mitigation. With fire, you don't have knockdown but you do have additional dots of damage, which also provides some mitigation in itself due to the fact that a lot of mobs with a sliver of life left to them get killed by it.

Here's a clip of my fire/shield in action. It's against +3 on a Council farm. I wasn't going all out but purposely slowing down a bit so you can see capabilities.

So I go on the side of electric/shield.

As far as survivability, either will be fine as long as you invest enough to softcap defense and get your DDR to a respectable level. What's respectable? For AV soloing and debuffing issues, you want to get to 95% for optimal survivability and to avoid casacading defense failure. For strictly farming purposes, it's not as important to hit the 95%, but I do it anyways because I am OCD about survivability.

As far as specifically AoE potential, I vote Electric/ due to the fact that you can dip into the Blaze APP for Fireball. Essentially, with enough recharge, you can alternate Lightning Rod and Shield Charge on spawns using Fireball for mop up at each. Electric/ also offers CI, JL, and TS for added AoE, though, you generallyu won't even need them for farming if you alternate nukes + Fball.

Now, the prior information is a direct reply to your exact question, however, this is not to say that Fire/ is a slouch. FSC is excellent AoE and pairing it with SC and Fball would certainly allow for excellent AoE and Fire/ has substantially better ST damage than does Electric/, so, for all around utility, I like Fire/.