Derek would've been a worthy win IMHO - that Cheshire cat was - I dare say it - a lovely zombie cat that wasn't too gory or frightening too.
But I can see Roy's winning because he actually had a slightly different idea on how a zombie turns into something else - his was based on the chess piece. I even caught it when I saw the original makeup (I was only able to see the reveals this week).
I just liked how the top three looks were probably the least gory - showing off their sculpting skills and paint job without the blood and such. From what I saw on the judge's faces, they seemed to feel that when the designers put so much blood on the models, they were trying to cover up stuff.