If the choices are between Synch, Iceman, Storm, and Rasputin. I would think it's probably iceman. He's a the only original X-man, we haven't seen assigned to any other book. Plus I am thinking about the time he basically saved the world on his own. He's definitely powerful enough to be an Avenger.
Honestly I think Synch and Rasputin should be put on a book together, and it's a shame Marvel isn't creating a new Generation X series, or an Uncanny Avengers type team for them to be on.
The only thing that really holds me back from thinking it's bobby is that
1.) he's in the Omega category but always struggles to hit that potential, meaning "mightiest" is questionable here. His most recent series had him spend the entire mini trying to keep his body from falling apart with the assistance of his boyfriend. The conclusion of which had his body blasted to bits again by some d list scrub and bobby going on a journey of slowwwwly piecing himself back together again. Without some miracle recovery he shouldn't be in any shape to be joining an Avengers squad for months.
2.) speaking of his minis, he's had a couple of recent ones, neither of which really lit the world on fire and even though he was "on" the marauders book they literally did nothing with him. Hard to see him as any kind of draw for Avengers.
Synch makes way more sense- he was a back to back member of the primary X-Men squad, with several interesting storylines centered around him. He works really well in any team setting but isn't usually in the leadership role, which works well if (like Storm) you need to justify why He's taking
orders from Cap, Tony, T'challa, or Carol instead of leading the squad.
He's also been incredibly versatile in how the writers use him- my man has potentially every metahuman power on earth and then some. Solve the aging issue and he's not just strongest mutant, he's strongest hero period.
Like a handful of X-Men that got sidelined to the Council (Exodus, Magneto) or The Five (Hope, Proteus, Eva Bell, Goldballs) Synch is almost too damn powerful to stick on your typical X-team without trivializing every combat encounter. He DOES work well against Avengers level threats though.
