More-so than mosts of the lists on this blog, this will be overly subjective. I've found that when it comes to choosing the best Transformers, it tends to fall upon the ones that people have an emotional attachment of some kind.
Also, Optimus Prime is clearly going to be #1 on any list, so we shall leave him out of this one.
I'm not including pictures, since most of the ones I've found are copyrighted, but I am linking each name to a wiki page that you can visit to see what they look like.
The Galactus of the Transformers universe, Unicron was the greatest threat ever faced by the Robots in Disguise. I remember being terrified by his massive size and capacity for destruction.
The first of the Transformers that was the result of combining other robots together, it was always exciting to watch any episode with the Constructicons because you knew that Devastator was coming.
8. Alpha Trion
One of the first Transformers, Alpha Trion was the Obi-Wan Kenobi to Optimus Prime's Luke Skywalker. Wise and self-sacrificing, Alpha Trion was everything that a mentor should be.
7. Hot Rod
The perpetual screw-up eventually stepped up and lit the darkest hour of the Transformers.
I loved the idea of someone who was friends with the Decepticons but was conflicted by their evil. And he was the coolest of the jets to transform half way and pretend he was a Robotech ship
His illusion power was one of the most underutilized in the entire series. I loved where he set up an illusion to make the Autobots look like Menasor.
A corvette that could also fly. How cool is that?
As slow-witted as he was brutal, Grimlock nevertheless tried as much as he could to lead his Dinobots to fight for the right.
On the back of all Transformer packages, it gives you their stats on a scale of one to ten. The tiny Brawn had a strength of nine. Like the DC Golden Age Atom, Brawn had a chip on his shoulder and was always out to prove his strength, often in some of the most entertaining ways. He is the only Transformer that I have on my desk as I blog.
The best of the Decepticons because not only did he have at his command some of the coolest minions like Laserbeak, Ravage, Rumble, and Frenzy, but he actually had a code. He was loyal to Megatron and was not always seeking to usurp him like Starscream. In fact, when Megatron is mortally wounded, it was Soundwave who rescued him. Soundwave could have been the leader but chose instead to remain loyal to his own code.