NOTE: There will be spoilers ahead. Proceed at your own risk. :D
Top Three Favorite Main Characters
This is going to be tough. My family will tell you I am HORRIBLE at picking favorites. I prefer to say I have many favorites.
1. Merlin, of course. Who doesn't have him as their number 1 favorite?
He's smart, he wants a world where there is justice for everyone and no one has to hide who they are, he's compassionate and he is loyal. He consistently saves Arthur and Camelot and is not rewarded or recognized for it.
2. Arthur and Gwen tie for second place.
Gwen is sweet and brave and not afraid to speak her mind when she feels strongly about something. I loved her relationship and loyalty to Morgana until Morgana turns to evil. It is beautiful to watch her transformation from servant girl to the Queen of Camelot. And her relationship with Arthur is perfect. He needs her so badly because she brings to him exactly what he lacks. My favorite season with Gwen was Season 5. Watching her in that season you would never have guessed she was born a servant. She is truly a great queen (minus what she does while under Morgana's power). She knows Merlin isn't stupid and shows him that she appreciates his loyalty.
Arthur is great! Sure he was a royal pain in the neck for a while. But you learn pretty quickly that he truly cares about Camelot even when he was being a pill. His growth through the series is fantastic to watch. And for those of us who have seen Season 5, didn't your heart just break at the end?
Morgana deserves honorable mention here because she was my second favorite character in Seasons 1 and 2. While I dislike the choices she's made and what she has become, I do understand why she did it. Not that it makes her any less despicable!
I love Gaius!! He is terrific!!! He is hilarious and the way he keeps Merlin in line is just what Merlin needs. Sometimes teasing him, other times giving him a shoulder to lean on, then bossing him around, then reminding him he is a powerful young man with a great destiny in front of him, and the next moment shaking his head because, will Merlin ever learn to listen?
Under Appreciated Characters
When Mithian was first introduced I was all set to dislike her. After all, Arthur belonged with Gwen, not her! But as the episode went on, I found myself liking her, and by the end of the episode she was one of my favorite minor characters. She is courageous, and insightful and she figures out Arthur and Merlin pretty quickly. It was sad that she truly did fall in love with Arthur because he couldn't love her back. Her last scene in The Hunter's Heart when she is saying goodbye to Arthur is one of my favorite scenes in the whole series. The dilemma she faces in Season 5 was heartbreaking and I'm so glad everything went well in the end. I wanted to see more of her in Season 5, but I'm grateful she was in one episode at least.
I spent most of The Changeling episode feeling so sorry for this poor girl. She was not to blame in the least for her clumsiness and strange behavior. When Merlin and Gaius saved her, I cheered. The wedding scene where she and Arthur agree they don't love each other and thus should not marry, no matter how politically advantageous it might be, is another favorite scene of mine. And her costume in that scene is STUNNING. Plus, she can beat Arthur in a horse race; riding a gorgeous horse to boot!
Geoffrey of Monmouth:
He is one of those background characters who is always there yet rarely noticed. While a little slow on the uptake sometimes, he is one of Gaius' closest friends and a trusted assistant to Uther.
And I'd just like to mention some of my other favorite minor characters: Aglain, Freya, William, Isolde, Hunith and Balinor.
Miss Melody Muffin