I live in the Netherlands and we don't really do halloween here...but if we did, I'd definitaly dress up as evil Morgana, she looks really awesome and I actually have a dress like that XD (don't ask me why :P)
We don't really celebrate halloween in Denmark, where I live, because we already have a holliday where we dressing up called "Fastelavn" ^w^ But if I should dress like a character, I'll choose Morgana, because she's a totally awesome badass girl... ;P atau maybe Gaius... atau Uther! xD THAT would be cool! ;P "Seize him! He's a SOCERER!" ;P