When I go from a role with heavy prosthetic makeup, which I've done quite a bit of as well, and then do a role where I'm not wearing any, I have to be conscious of toning everything down. Because when you're wearing prosthetic makeup, of course, you have to really move your face a lot more to convey things through the makeup.
But things such as 'Harry Potter', all I can do is shape my character, seek the director's approval on that, and basically take it from there. Professor Flitwick in 'Harry Potter', I kind of defined how I saw him from reading the book, and luckily that matched up with the director's vision.
I wouldn't say one is easier or more difficult, but when you're inside a costume and a mask, you have to endure heat - and, often, difficulty seeing. The vision is not very good in a mask. And you have to cope with that, as well as trying to think about this character.
If you stood me in a costume next to a computer graphic of the same-looking character, I think there would be a difference. And many movie fans I've spoken to would rather see an actor in a costume than CG.