Again, base it on whatever you want. (Mine are all G1, by the way.)
1) Grimlock: Preferably the comic version, where he was the coldest-blooded and most ruthless of all Autobot warriors, and who frequently clashed with Prime (despite their being characterized as old friends).
2) Optimus Prime: I don't think this needs any explanation. Optimus Prime is the hero.
3) Jazz: The infatuation with Earth culture made Jazz the coolest of the first-generation Autobots. That, and his toy was probably the best overall.
4) Bumblebee/Gold Bug: It's hard not to like Bumblebee, unless he's turned into a mute Camaro.
5) Nightbeat: A later character, but who was sort of the "private eye" of the Autobots. In later stories, he became more important as several important mysteries came up at once.
6) Fortress Maximus: Prime's closest equal in terms of personality, though maybe even more pacifistic. Binary bonded to Spike Witwicky, to boot.
7) Hot Rod: Prior to becoming Rodimus Prime, he's a great everyman character in the movie. In the comics (old and new), he's a rash young warrior who is one of the best, but tends to bite off more than he can chew.
8) Ratchet: Next to Prime and Grimlock, possibly the most important character in the comic. His frequent underdog run-ins with Megatron were some of the best storytelling in the series.
9) Cliffjumper: Bumblebee with a 'tude, voiced by Casey Kasem.
10) Kup: Moreso in the comics where he's an older warrior who's been battle-hardened until he's almost as cold as Grimlock. In the movie, he's a little annoying.
1) Bludgeon: A martial-arts mystic who has a pretender shell to resemble an undead samurai. It doesn't even matter that the character is cool. He wins it just on concept alone.
2) Starscream: Easily the deepest Decepticon, if not Transformer, in the series. It's no accident that everyone remembers him.
3) Megatron: An unstoppable juggernaut of evil (he even turns into a Nazi pistol!), only vulnerable to his own insanity and megalomania. The perfect counterpart to Prime.
4) Ravage: Silent, cunning, heartless, and brilliantly intelligent. If all Decepticons were like him, they'd have won this war millions of years ago.
5) Scorponok: A generic Megatron surrogate, until he binary bonds with an alien human who turns out to have a conscience and who takes over his personality. His death scene at the hands (err, feet) of Unicron is brilliant.
6) Thunderwing: The only Decepticon to ever hold the Matrix. He's here mainly because a vampire Decepticon who doesn't look stupid (ahem, Bomb Burst) is almost as cool an idea as the undead samurai.
7) Shockwave: The cold, calculating foil to Megatron. Where Starscream is mostly talk, Shockwave is all action. And he has the patience to wait a few million years for a given scheme of treachery to come to fruition.
8) Soundwave: The best thing about Soundwave is that, although he's almost perfect at hiding his thoughts, he's clearly fiercely loyal to Megatron but wouldn't think twice about betraying any other Decepticon. Well, except for his tapes.
9) Ramjet: A crazy plane who likes to ram stuff. For the kid in all of us.
10) Ratbat: The accountant leader (for a while) who runs the earthbound Decepticons with ruthless efficiency. If one of his schemes hadn't been a carwash that brainwashed people, he could've scored higher.