8. Grimlock (G1)
The Dinobots have always been somewhat of wild cards within the Autobots, especially their leader, Grimlock, and due to their ever-changing origin story, it's hard to say whose side they were initially on.
In most versions of the story, Grimlock and the Dinobots were created by Transformer scientists, but that could either have been Wheeljack on the Autobot side, or Shockwave for the Decepticons. While the 'Decepticons experimented on them' plotline explored in the video game Fall of Cybertron is a good one, the far more interesting one, in my opinion, is that of the G1 continuity.
Created by Wheeljack, the Dinobots were meant to protect the Autobots, with Grimlock being the strongest of them all. Yet, Grimlock - believing that the strongest should lead - was tricked by Megatron into serving him. He may have been strong, but he certainly wasn't the sharpest. Thankfully, through selflessness, Optimus demonstrated the true strength of a leader and convinced Grimlock to rejoin the Autobots.
From good guy, to bad guy, to good guy. Haven't had one of those yet.