Ok, Magnus is my fav but he's kind of a given, but here are my reasons:
1) he's Magnus, need I say more?
2) he's funny
3) he's gay
4) he's just enough of an a** to still be nice-ish (it's different from jace...it just is...)
5) he's just plain AMAZTASTICALLY FANTABALISTIC!!! 3nodding

Not counting Magnus(cause he makes it really unfair for the other characters), Simon's my fav, and here's why:
1) he's a nerd. I have a special place in my heart for nerds heart
2) he's just adorable...in a nerdy kinda way lol
3) he's a musician. Since I too am a musician, he is therefore awesome.
4) he too is funny. The banter between him and Jace is awesome.
5) he's not some useless random friend that is usually in books like this. Even when he was a human he helped.

And that's why I luvs Magnus and Simon! whee