fine, since we're talking about solos, i'll say my favorites.
亀梨和也 - 絆 (Kizuna)
赤西仁 - ムラサキ (Murasaki) (though, i get a laugh out of "ha-ha" too)
田口淳之介 - サムライ☆ラブ☆アタック (Samurai☆Love☆Attack) (LOL. I LOVE IT.)
田中聖 - Make U Wet
上田竜也 - Love in snow
中丸雄一 - key of life
i think the most consistent person with solos is Ueda, actually. which probably explains why he is the first to get solo concerts, LOL. i love his solo works, but i regard him as my least favorite member.
oh, i just realize my favorites either come from KAT-TUN Live Kaizokuban concert or the ones on cartoon KAT-TUN II You. haha!