If we're talking about favourite characters in the movies, my top three:
1. Eustace. That kid was hysterical. Such a prat, and unlike Edmund, he still was obnoxious once he started to mend his ways. He made me laugh everytime he had a scene. Period. I can't help it, I just love the mean ones. I happen to adore Draco in Harry Potter, too.
2. Puddleglum because he was so gloomy but he somehow never came across as depressing. I loved that he was so wise about everyone and everything around him but when it came to himself he was entirely clueless.
3. Reepicheep was great in these (even though the costume was less than spectacular). John Rhys Davies (the guy who plays Gimli in LotR) said the best thing about his character was that he didn't realize he was small. Take that same statement and apply it to Reep. That's what makes him so much fun.
If we mean the books, my top three:
...okay, so they're exactly the same. I'm boring like that. I also loved Trumpkin in both, just not as much as the others.