At first, I felt that Xemnas was harder, but after playing through KH1 again on Expert mode, I feel that Ansem SoD was the harder one after all. I took on KH2 on Proud mode and for the most part, Xemnas was easier and I was about the same level as on KH1. The only problem I had on my first play-through was being confused on the second to last part at first. It took about an hour to figure out what I was doing wrong. Fail. On subsequent play-throughs, Ansem SoD has proven to be harder on Expert mode than Xemnas is on Proud mode.