Team of 3 suggestions!

Based on your Brute:
Cold or Thermal are the best options for ELA. Cold will be the better long-term option, Thermal will make the pre-SOs, pre-Energize, pre-Tough/Weave/IOs much less painful but will be weaker in the long run (but do note: "weaker" as in "a man with $950,000,000 is poorer than another with $1,000,000,000").

I would suggest Pain Domination, Kinetics, or Sonic Resonance as being runners-up that would be a little bit rougher. Sonic Resonance will sort of plateau early and not get much stronger after Sonic Dispersion and Disruption Field but it also won't become obsolete. Pain Domination will spike early but after said spike, until it gets its late-game goodies like World of Pain, Anguishing Cry, and Painbringer, it will be one of the weakest options. Kinetics is, well, Kinetics. You can't really badmouth it except that it can be rough on the user when played well. And if you ever broaden your team on some nights, your Dead Cat© Brand Member-Seeking Device™ will be able to swat a couple out of the air very easily, so it's not exactly crucial to have your own (unless you expect good performance--PuGging is always a crapshoot).

It's more-or-less a question of how much suffering you want to impart on your third. Cold is the absolute best for self-survival and end-game performance on your existing layout. Sonic Resonance will be rough on the Corr (Dis. Field and Son. Disp. together suck endurance like nothing else), as will Kin as I've already said. Pain will be more or less indifferent (must...resist...puns...).

And for the love of all that is holy: Get and slot Fault up right away, it's not just useful for you! If you learn to love and use Fault, ELA's shortcomings will make it easier on your supporting third and make the game overall much easier. It really is that good.

As for primary... Well, I'll suggest the obligatory Sonic Attack. -Res is always nice. However, Radiation Blast can be extremely enjoyable, particularly once you turn Neutrino Bolt into a proc cannon--Neutrino Bolt giving off five numbers (regular, scourge, Apocalypse, Shield Breaker, Lady Grey, and possibly -Res from Achilles' Heel) is immensely satisfying to see, even if it's not from you. It also can be satisfying in the "I always have something I can do...and I have endurance to do it with!"

Your team is a little lacking in AoE. I might suggest the Stalker, if they're set on playing a Stalker, go Electric Melee or Spines (although I can't attest to the strengths of the second personally, so this is just an armchair estimation). If they're not totally set on Stalker... Another Corr or Electric/Shield Brute will also do quite nicely.

The reason I'm dubious on the Stalker is that after awhile, having a more ST-oriented set will likely make the Stalker feel less powerful and more like a third wheel, particularly when an ST-focused build like an SM/ELA Brute starts to come into its own. But hey, your mileage may vary.