I can only say that I seriously listen to J-Pop. I can't really argue against K-Pop considering I do like Girls' Generation, but that's about it. I don't really listen to K-pop, but I like what I've heard so far from a few other random artists. So, my stance is pretty neutral.
Merging the K-Pop vs J-Pop thread with this one since K-Pop definitely needs to be discussed in full.
I listen to K-Pop quite a bit, but the only groups I listen to with regularity are Girls Generation (SNSD), GIrl's Day, and SHINee, since I'm too lazy to download the discography for other artists (and I don't have enough space on my computer) When it comes to K-Pop, I tend to prefer pop/hip-hop groups instead of solo artists because they feel a little more fun and upbeat. I suppose the lack of boy/girl bands in the US these days is what has led me to listen to this genre of music.