Generation 1: Optimue Prime(I love the trailer)
Beast Wars: Megatron
Robots In Disguise: Omega Prime
Armada: Unicron
Alternators: Mirage
Binaltech: Arcee
(Newest one I got)
Energon: Omega Supreme
Cybertron: Optimus Prime
Classics 1.0: Too hard to choose. Basically all of them are my favourites especially Henkei Version.
Movie: Deep Space Starscream
Animated: Snarl, Prowl(Don't like most of them in the line.)
Universe 2.0: Silverbolt(Seriously, it is the best in the line so far), Prowl. Tankor is good, but too bad it isn't a Voyager.
Masterpiece: Megatron.