When I was younger my favourite character was Bumblebee...Always loved him and his little super-deformed Volkswagon was one of the earliest TFs I can remember getting...
I was appalled at the notion that he WASN'T going to be a VW in the movie, especially since I thought the new Bug would have been perfect (though at the time I wasn't aware of some of the understandable reasons why they didn't / couldn't go with Volkswagon) but then I actually SAW the Camero and simply no longer cared because that car was BEAUTIFUL...And the original deluxe Concept Camero Bumblebee is still probably my favourite figure from the movie line
Now that I'm older though, I have developed a very deep appreciation for Hot Rod and I'd say he's my favourite nowadays...It was the classic story of the most unlikely hero getting the unexpected (and likely unwanted) burden of ultimate responsibility, yet stepping up to the plate to handle it as best he could despite improbable odds and an impossibly huge shadow to try and get out from under...I just love the idea of that character...And I LOVE his toys (G1 Roddy excluded of course)...Hot Rod had a really cool cybertronian racecar alt-mode...Red with flames is always a win

I have a pretty nifty Hot Rod collection built up with only a couple missing...The alternators repaint / retool was just gorgeous...And Classics Rod is still one of my favourite figures period...
Second favourite character, I think, is Shockwave...He's had slightly different personalities / functions in the different continuities but he's always pretty damn cool...Even though he really got the shaft in the G1 cartoon by always being stuck on "Guard Duty" (God bless you,
Dr.SMOOV !)...And his toys have almost always been awesome...G1 Shokwave was undeniably one of the coolest figures of the bunch...He's also one of the best alternators, and even his Energon figure was pretty cool...(And I'm LOVING my new grape-a-licious Animated Shockwave repaint)