As of now:

1) SUPER JUNIOR
2) 2PM
3) 2AM
4) TVXQ
5) Kana Nishino

Currently:

1) G-Dragon
2) Big Bang
3) Ayumi Hamasaki
4) Wonder Girls
5) Tae Goon

Now :

1. Ayumi Hamasaki
2. alan
3. Big Bang
4. TVXQ
5. I can't decide between Wondergirls or SNSD :laugh

1) BREAKERZ
2) DAIGO STARDUST
3) Kanon Wakeshima
4) Matsushita Yuya
5) BENI

1st 2 will never ever change as far as I'm concerned 8D

changed again omg!

1) 2PM
2) Super Junior
3) NEWS
4) Kana Nishino
5) 2AM

1. Namie Amuro
2. Hikki Utada
3. Ayumi Hamasaki
4. Gackt
5. ayaka hirahara

i only have top 3 right now :P

1.EXILE
2.LOVE
3.Ayu


maybe no.4 is SPEED

^ lol Pei Yee x)

anyway

1) BREAKERZ
2) DAIGO☆STARDUST
3) ON/OFF <3 <3 <3
4) Matsushita Yuya
5) BENI

1. 2PM
2. Kana Nishino
3. BIG BANG
4. TVXQ
5. 2AM

01. L'Arc~en~Ciel
02. Ayumi Hamasaki
03. Miliyah Kato
04. immi
05. Kana Nishino / Kuroki Meisa

1. sifow
2. Ayumi Hamasaki
3. Koda Kumi
4. Namie Amuro
5. alan / Ami Suzuki

1. Koda Kumi
2. Ayumi Hamasaki
3. Ikimono Gakari
4. Ayaka
5. Shimizu Shota

1. Utada Hikaru <333333333333333
2. Do As Infinity
3. Ayumi Hamasaki
4. Namie Amuro
5. BoA/Crystal Kay/Thelma Aoyama/Jyongri.... they are all at the same level lol!

Changes... again:

1) Kana Nishino
2) SUPER JUNIOR
3) SNSD
4) BIG BANG
5) 2PM

this is definitely not my all time (a few of those artists are currently missing from my top 5's). but lately its definitely this.

J-pop/K-pop

1. Eiko Shimamiya
2. Ayumi Hamasaki
3. MELL
4. JASMINE
5. Loveholics
(and random I've Sound girls come after)

J-rock
1. Nightmare
2. An Cafe
3. SuG
4. vistlip
5. MUCC
(and then Ayabie, GazettE)

Change of top 5 for me again!

1. BIGBANG
2. G-Dragon
3. Ayu
4. Taegoon
5. Wonder Girls

01. Ayu
02. 2PM
03. Super Junior
04. SNSD
05. CN BLUE

I'll do a better list (my other one wasn't much precise):

J-Pop:
1) Ayumi Hamasaki
2) Koda Kumi
3) Namie Amuro
4) BoA (I can consider her as jpop, right? xD)

J-Rock:
1) LM.C
2) D
3) Kra
4) DIR EN GREY
5) BREAKERZ

Korean:
1) f(x)
2) Super Junior
3) SHINee
4) SNSD
5) CNBLUE
6) FTIsland

1. Kana Nishino
2. Kuu
3. Namie
4. 2PM
5. Ayu