I think though that I would start with it being Microsoft, and so they wouldn't have to have an internal studio working on the project. (In fact, Insomniac was not owned by Sony at the time when Marvel came calling to make a game together, and Sony picked Insomniac despite that studio making moves towards independence and away from Sony at the time; they had just done Fuse for EA and were working on Sunset Overdrive, but there was no bad blood fueling Insomnaic's move to make new friends plus they still had ties with Sony for Ratchet, so it worked out.)
If we're talking something big like a Hulk game (which is the most obvious guess at what MS would have chosen, as even way back when we heard that Marvel was taking pitches for games and Sony got Spidey everybody immediately jumped to assumptions that the big green guy would be on Microsoft's big green box,) Insomniac is as has been said a solid choice. Of internal studios at Microsoft in the 2013/2016 timeframe, Black Tusk/Coalition would have been a choice (they were moving onto Gears from their original IP attempt just around that time, this could have caught them before the change... and then, maybe People Can Fly could have been retained for Gears, but that's all an alternate timeline that may or may not have been better than Gears 4/5,) Twisted Pixel was never AAA but they have mainstream talent from and could have been pushed in unexpected ways after fucking around with LocoCycle and The Gunstringer, Lionhead was still existent and could have been saved with a mainstream title, and then crazy idea but Rare had "owed" the Xbox audience a mainstream monster hit since its purchase and they certainly had the talent to do anything, plus that would have been the serious name that Marvel would have liked to see to rep its brands. As far as third parties, take your pick, but in that timeframe, MS was working with People Can Fly (again), Double Helix, Crytek, Ruffian, Remedy, Sumo Digital, Splash Damage, Armature, Remedy, and Asobo, among others who might have been considered.
I don't know if there was really a blockbuster formula for success in there, but then I didn't really think Insomniac's approach to game design would have been right for Spider-Man (and am still questioning how they will fit as a Wolverine developer,) but the choice was obviously smart on that one.