Lol, that sphere movie was kinda fun. I liked the particle effect (of course). It was probably a good exercise to figure out the animation controls. :)
As for your Q, I think 3D is the most fun to animate, but that's just a preference. I really like the sculptural aspect of it and the complete freedom to change things at any time. I like to tweak things as I go along so it feels really free to me.
A lot of people here seem to have a prejudice against it (see above comment lol), but I think that's just because there's so much of it being done in movies these days. There's a lot of really interesting things you can do with it that haven't been explored, especially with non-photorealistic rendering and the like.
I like the look of 2D, but I really don't like doing it. It's incredibly time consuming, and it feels frustrating to me to keep drawing the same thing over and over. I've gotten some nice results with it, but it took me way longer than any 3D stuff has, even considering the prep time. I don't think it's a dead art form, by any means, but I can understand why people turn away from it in cinema because it's much more expensive to produce considering the manpower needed.
I haven't tried stop-motion and I don't know if I ever will (I don't think I'd have the patience for it), but, again, I do like the look of it. It's perfect for a surrealist atmosphere since the movements aren't quite perfect. There was a stop-motion movie of Peter and the Wolf I saw a little while ago that was absolutely amazing.
PIED3
2d, then claymation, then 3d. 3D is horrible.
Xennethy
Yeah I also enjoy working on clay when I'm working on stop motion. It's easier to animate then other materials.
And i think 3D is just more technical.