Hmm, funniest~
Hana Kimi is so funny. Hana Yori Dango has its funny moments but it's like when I hear the theme songs somewhere I start to cry because it's so good.

Kimi wa Petto is funny also~ Maybe. If I remember right. But it was cute, not sure about the funnyness.

Everyone says Stand Up! was so funny~ Well for me it was, it was, but I was a little bit shocked always while watching it.

Gokusen is funny. Especially the first season. But every season has
its bonuses.

1 Pound no Fukuin's first episode was pretty funny. That "gutless glutton" was the best.

It really made me laugh so hard.

But it was also a bit boring to me~
Nobuta wo Produce was funny, it made me laugh many times~
And Yuukan Club has so many funny moments.

Zettai Kareshi is funny also.

Especially Night's "Riiko, ore sexy?"
So, my list:
Hana Kimi
Hana Yori Dango
Gokusen
1 Pound no Fukuin first ep.
Nobuta wo Produce
Yuukan Club
Zettai Kareshi
Funniest J-dorama would be Hanazakari no Kimitachi e. 
All thanks to Nakatsu. 
"Ore wa homo janai, homo janai, ho-mo ja-na-i"
AGREEED!