BumbleBee because he is easy to transform
What is your favourite transformer?
Star scream -
Because he was always trying to take over the deseptacons and kill megatron.
Okay, this one has so many answers (only because I watched the cartoons and the movies):
Transformers movie (Michael Bay): Brawl (the tank) and Blackout (the helicopter)
Transformers Revenge of the Fallen: Jetfire
Transformers Dark of the Moon: Probably Sentinel
Transformers Age of Extinction: Autobot Hound (that guy was amazing)
Cartoons
Transformers Robots in Disguise: The Railway Runners and the Constructobots
Transformers Armada: The Street Action minicons (Grindor, High Wire, and Sureshock)
Transformers Energon: I'd have to go with the combiner bots (Bruticus Maximus, Constructicon Maximus, and Superion Maximus)
Transformers Cybertron: The entire Cybertron Defense team (Scattorshot, Red Alert, and Hot Shot)
I started watching from the Robots in Disguise series so that's all I've got.