Japan has a nice respect for DJ culture so you have a lot of nightlife options. Dance music and hip hop are well represented there. There's also great restaurants where you can get just about any type of food and not have to wonder, 'Is this dog, hmm... maybe cat... goat... no, maybe Yak!' I can't forget the bars where even the stuffiest businessman will let it all hang out! Sapporro! Ya gotta love a 64 ounce glass lined aluminum can!
Japan has tons of different types of areas like the Ginza district which is nice for the sightseer's and Shibuya which is filled with hot little nicely tanned rappungi Japanese babes... and cool bars and small clubs too.
They are also a relatively wealthy country compared to China. This changes the criminal element. You might get mugged in Japan but China is still a place where a woman can still get kidnapped and sold.