Onslaught.
A lot of other key options are really missing awakening but onslaught arguable needs it the least. Jean Grey would probably be the next best and personal preference would put her on top.
This is an interesting one. I for one hate Onslaught's play style but he is a massively high Prestige champ.
And I HATE that that matters now… but it really does. I have both him and Jean unduped and would rather take my Jean to R4 for the fun but having Onslaught there is enticing too.
Ironheart at r4 is amazing. She's an absolute utility queen, and handles so much; especially if you run Despair/Inequity.
She doesn't have a reputation for being fast; but that only matters at all in Battlegrounds; and she's still perfectly useable there; since she's got a kit that can handle defenders like Bullseye, Photon, Zola, Jean Grey and Onslaught easily, with high health finishes. You may not see her at the highest level; but she's great if you find BGs a challenge.
She can shut down nodes like Stun Reflection, and anything that triggers on Parry (like those annoying Disorient and Falter nodes that Kabam has been fond of, lately).
Currently I've just taken mine into Raids, and she's easily hitting the 12% damage cap, and finishing with a nearly-full health bar, even though my teammates have only gotten me 4 or 5 charges.
And for Necropolis, she carries the #Ten year challenge tag and is immune to reverse controls… I used her to Power through Silver Centurion (genuinely nasty, if you don't have a plan) and her SP3 Power Drain was enough to make him very manageable.
Definitely a worthy rank-up, and I've never regretted mine!