I think it's just a totally different style of writing. If you're good at getting inside characters' heads and writing in their voice, then first person is probably easy for you. If you prefer the more flowery, descriptive style of writing, third person is probably easier. I think it also depends on the character narrating, if you're doing first person... some characters are better narrators than others, you know?
Personally, I almost always write in third person. I like it because it's not as limiting, and it allows me to be a little more flowery at times without it sounding unrealistic because no one actually thinks/writes/talks that way.
That said, I'm reading five different books/stories right now, and all but one of them are written in first person, so now I'm in that mode. I'm very easily influenced by what I read LOL.
Poll
