Answer
It’s obvious that I listen to a lot of Japanese pop music besides some of the good/older american pop and other genres since I have been listening it since 2004. While I haven’t listened to any Korean pop, I tend to not like where they are heading since their songs have become too manufactured with the overuse of Autotune over pure talent. Considering that K-pop is dominated by idol groups more so than J-pop, it definitely generated a lot of harsh criticism. Then again, J-pop is not guilty of it, but it’s not as predominant as idol groups like the AKB48 don’t dominate the Oricon charts and you actually see individual singers. Also, they have a pretty active indie scene.(See THOUGHTS ON THE EAST ASIAN “IDOL CULTURE” PART 1 from Anime Instrumentality and you probably know what I’m talking about)
There is one good thing about JPop over K-pop… at least their music styles are more diverse than having thousands of redundant bubblegum pop that you probably get tired of.
As for my favorite singers, I like Kalafina, Lia, Maaya Sakamoto, and Nana Mizuki to name a few… There’s more, but I don’t want to overwhelm this answer with a big list of artists since its subject to change)
I wonder why could stay alive on the top the bands in East Asia like Backstreet Boys ( a bunch of handsome male group) or Spice Girls (female, but sometimes with a million girl, like in the Morning Musume), until here they are outdated. For example the SNSD and the 2PM is more and more popular in Japan even if they have their versions already and don’t give any new for the music. They are just mass factored idols, they can be popular, but the managers easily throw them out from the band if they are get old. Some latin pop group (Menudo) have many similarities to this.