Decepticons transform into cooler vehicles.
Decepticons. The Constructicons and Predacons were freakin awesome. The Dinobots originally took orders from Megatron.
Autobots have Omega Supreme. They win.
The few, the proud, the likely insane, Metro-Atlanta bicycle commuters.
Decepticons. Come on, Megatron, Galvatron, Sound-freakin'-wave? None of that Michael Bay crap, either.
They've surely all been replaced by carbon fiber models by now.
The search for inner peace continues...
Fortress Maximus and Metroplex are big. The answer to the OP, might be neither. Unicron is pretty badass.
i've got to go with the Autobots, if only based on the current All Hail Megatron comic miniseries.
astute readers will point out that in the series, they've had their collective ass handed to them by the Decepticons.
but the fact that it has made Perceptor seem like a bad-ass gives them the win.
"Perceptor - Perceptor is scary. When did Perceptor become scary?" - AHM #6
More of a COBRA man, myself.
Decepticons are waaay better.
The guy who did the voice of Starscream died of a cocaine overdose. No joke.