Alec- Mundane... He calls you this every once in a while depending on his attitude depends on how you should take it...if you have pissed him off or made him mad he says it to refer to you as being human...or if he's in a playful mood and wants to get you going to call your Mundane...
Jace-"Love" He loves the way your face lights up when he says your nickname... You question why he calls you that but he says that he didn't know how to love someone, Until he met you.
Simon- Angel.. He calls you angel because he thinks that's sometimes he's bad and nothing but bad... But he calls you Angel to make him see the goodness in the world.