This is hard... I can never love just one so there's a bit of a list. Skyfire, who I wish was more than a taxi in G1. Than there's Swoop and the Aerialbot group -- starting with Slingshot... For some reason he's a major favorite of mine.

For TF:A it would be Jetfire & Jetstorm, and for Armada it's a tie between Jetfire and Starscream. Than for Cybertron Wingsaber was my fav. (Yes, this list could get bigger. No, I can't figure out how to narrow it down.)

 

If it was G1 Only, I would say Springer, but counting the Movie-verse, I would say Jetfire.