As for his Castiel, I'm most partial to the BAMF Cas at the beginning, from his amazing entry to carving a banishing symbol in his own chest. Misha did a good job portraying an angel unfamiliar with the up close behavior of people and looking at them as though they were microbes under a microscope. I appreciated his struggle to rebel against Heaven.
One of my favorite scenes was from The Monster At the End of This Book where Cas tells Dean how to chase off Lilith without really telling him. That look.
The early Cas was used sparingly for comic relief in a way that worked with the characterization and didn't just mock him. It was slapstick and silly but the scene with the cellphones in My Bloody Valentine makes me laugh anyhow.
I get frustrated with the whiplash personality changes they've put us though since S6. I hate that he is so easily led but I suppose if you have spent your life having someone else make the decisions for you, you're bound to screw it up when you finally get to make them for yourself. I wish he'd learn from his errors. I hope they can do good things with him as a human in S9. I liked him in The End when he was essentially human and would be ok if they took him in that direction. I'm going to struggle if it's handled like the grocery store scene with him shopping for pie in S8. He's been observing humanity for thousands of years and hanging around with the Winchesters for four and I think he's smart enough to have picked up the workings of an egg.
Caps from homeofthenutty and the Misha photo from his twitter.