My top 10 faves are:
1.) Starscream
2.) Blitzwing
3.) Waspinator
4.) Bumblebee
5.) Sari (some people think she's a Mary-Sue, but I like her anyway.)
6.) Bulkhead
7.) Prowl
8.) Optimus Prime
9.) Lockdown
10.) Soundwave
"Some people outsmart me, maybe. But can they outsmart bullet?"- Heavy (Team Fortress 2)
My top favorite was Ratchet. He became such a great, deep character, even though his basic role at the beginning was just to be an angry old war veteran. I consider him to be the Dinobot of TFA, not because of any similarities between their personalities (since there aren't much, if any) but because of the great characterization and development they received -- Dinobot in-story, and Ratchet through his flashbacks.
I don't think I could choose a top 10, though. There are so many memorable characters to choose from, some for their quirkiness and some for their engaging personalities and development arcs.