I have done both. I love the tiny humans the best. That being said, when you treat tiny humans, you also treat the ENTIRE family, that can get complicated.
Adults, you assume they are rational and able to convey their complaint to you. Not always true. Also, I came from a straight ped's ED. I went into adult ED and I had to relearn myself. I had minimal cardiac experience (YIKES) and NO Stroke experience. That was a little scary. I went from being int he base of a large hospital to being in the middle of a building with NOTHING. A lot of these factored into my transition.
That being said, I like my older population, I love kids. I see a lot of similarity. It's all about what your comfortable with. With kids, many nurses are initimidated to stick them because they will cry, many are scared of invasive procedures on kids. With adults, well than you have the person who hyperventiliates themself.
It's really just preference.