I like Optimus Prime. Yes, he's epic and grand and powerful... but I like him because he doubts. Doubts himself and his ability to guide the autobots, doubts the war/reasons behind it and sometimes doubts their human allies. It makes him seem more human and it's his biggest flaw. Megatron feeds off of it constantly and it's most obvious in the TF:A universe because it's physically embodied by Blackarachnia and Sentinel Prime. It's not the most obvious flaw, but he probably carries a lot of regret, too. Doubt and regret is constantly at the forefront of his mind, I'm sure. He's fueled by both emotions. When people die, things go sour, the troops are unhappy, it's Optimus they turn to - he can
never falter or slip up - so I'm sure it's an unimaginable pressure.
Ratchet is my favourite from any continuity; grouchy, boisterous and for the most part, a softy. He likes fixing up mechs, but always gives'em pit for injuring themselves. He doesn't like seeing careless injuries, and takes s**t from no one. Ratchet looks forward to the day his services are no longer needed, when bots are no longer at war and constantly injuring themselves. He joined the autobots to help other 'bots and end the war. He sees Optimus as the fastest way to peace. Ratchet is worn and old, mostly. Tired of the war, tired of pain... tired of always fighting. It seems sometimes like he's ready to be put to rest, but really can't be because he's needed. I feel a lot of pathos for him.
As for Decepticons, I like Soundwave. "Cries and Screams are music to my ears." He's very interesting in his social interactions with his fellow decepticons. There is
always opportunity in confusion, using whatever he records to blackmail other 'bots. He cares for very little besides his cassettes and has a strong dislike of Blaster. He rarely ever shows any form of emotion except distain. Powerful and a man of VERY few words, he expresses himself by what he doesn't do - and - doesn't say. Actions, words and lack there of define him.
For those who like Starscream (there seems to be quite a few...)
Starscream glomps Megatron and
Starscream discovers Car washes......XD