Photoshop animation quality on Youtube

I've created a series of animated sequences in Photoshop CS5. The look fine when rendered to Quicktime...in Quicktime. Uploading them as a test on Youtube is where the problem lies. If I go with YouTube's recommended settings (incl H.264 codec), the black lines look jagged, not smooth. But the sequence plays just fine. When I go with the Animation codec, the sequence looks much better, but gets choppy or hangs up. I have to add that I'm editing in iMovie '11, but this happens whether exported from iMovie or directly from Photoshop. Any help would be much appreciated. Thanks!