After the sneak preview, these are the characters I think are best for each slot:

Cost 7:
Best: Aquaman, King of the Seven Seas
Runner up: Superman, avatar of peace

Cost 6:
Best: Gorilla Grodd
Runner up: Ocean master or power girl, not sure

Cost 5:
Best: Scarecrow (fearmonger)
Runner up: Martian manhunter

Cost 4:
*Best: Poison Ivy (updated)
Runner up: Oliver Queen

Cost 3:
Best: Aquaman, Arthur Curry
Runner up: Captain Cold, Leonard Snart

Cost 2:
Best: IQ, Ira Quimby
*Runner up: Red tornado (updated)

Cost 1:
Best: Copperhead, Slithering Assassin
Runner up: Ted Kord <> Blue Beetle

So, what is your list?

Update:

Best plot twist: Glass jaw
Runner up: Counter Strike

I'd replace Counter Srike with Air Strike. It's much better. As far as two-cost charaters go, I'd say IQ and Red Tornado.

The 7-drop that gives locations, "exhaust this location >>> power up target character" is very good.

I'd pick Martian Manhunter over Scarecrow right now and I think you're overrating The Joker. What about that Nimrod 4-drop?

Captain Atom & Hal Jordan were used a lot on 6 at my sneak peak.

Rama Khan will force you to include unwanted locations. That is not cool.

Martian and Scarecrow is a difficult decision, but I would rather have scarecrow and remove pesky cosmic counters and +1/+1 from counterstrikes. Giving em to your 6 has a greater effect on the long run than Martian. As I see it, Scarecrow is good on and off initative. Martian is extremely good off initiative, but just ok on initiative.

Sometimes, Hal Jordan would do nothing meaningful, specially if your opponent made his formation with care. And Atom gives +1 to other attacking characters, but against a bigger 6 drops than him (power girl and ocean master), that is hardly an adventage, really. I would rather get metamorpho instead of Hal or Atom.

Darkseid at 5 was awesome. He was especially unbelievable on turn 7. Attack down with the 7, then ko him to give someone -7 defense. It's a game ender.

Also, tasmanian devil was a pretty sick 5 drop. Especially the game that he got dropped on turn 8. 15 atk. I stun your 7 with my 5, yes that's fair.

Though I wasn't at the sneak preview myself, the one card that I think really has the ability to swing the tide of a sealed game would be balance of power. Though it doesn't have any hope in constructed, it's ability is just devastating in sealed.

Top commons

Trial by fire, Wall of Will, Balance of Power, Gorilla Grodd, Ultra-Humanite, Air Strike,4 Drop Batman, Reform the League, Glass Jaw, plasma blast, Hawkman, JLI embassy, Scarecrow and MOST IMPORTANTLY Death trap.

Top Uncommons

Safety in Numbers, MM5, Crimson Fox.

Where is your 8's? lol. I imagine something like Dr.Fate and Martian Manhunter.

You won't have more thay 1 cost 8 character to pick.

Ummmm

All too easy. Was it fair for my 2 drop to take down your 6?

neron was pretty good for me at 6. combining him with scarecrow to move the counters around it was pretty hard for my opponent to stun my characters

I liked the other scarecrow (pyscho psychologist) at 5 or 6 with his boost...brutal

The hidden batman was a decent 4 drop for me....when people missed their curve he was devistating...

Glass jaw and counterstrike worked well...air strike was used well in the one match I lost....(he had 2)

I am A big Fan Of Grodd.

CounterStrike and Balance of Power are good and Great Together.

On a Side not how come we dont have a Equipment that gives you Activate>> Stun Someone with a Cost of 2 lower than Than the Cost you activated?

I largely agree with this list, assuming you just forgot Rallying Cry.