Archer, well without him there would be no Federation.
That might be taking things too far. Without Archer, Starfleet would have planted someone else in the centerseat. The series of events that transpired leading to the Romulan War and the later Federation would have still happened, even without Archer's existence.
The crew of the Enterprise likely would have been identical, minus Archer, and plus (imho) Hernandez.
Looking at the series, Hernandez would have been the obvious second choice for the Enterprise's command. With another Captain chosen for the Columbia.
I thought Gardner and Robinson were the other choices, with Soval preferring Gardner.