Am living in Tokyo at the moment, and went to Beijing last Golden Week (early May.) The two countries are very different, and I'm hard pressed to recommend one over the other. China and Japan are almost polar opposites. Your dollar will go so much farther in China, unless you stay in Western oriented areas, so it gives you a certain freedom to do things. Even getting to Kyoto from Tokyo is quite expensive. I really enjoyed the Great Wall, which is more impressive than even the shrines in Japan I must admit. Since you'll only have a week you won't really be able to visit the more isolated parts of either country. The people in Japan are super-polite and you don't have to worry about getting ripped off. I'm sure I paid more than the locals in China, but I didn't mind since it was so cheap anyway. As you can see I can't choose either, but would lean towards China because it is such a dynamic place right now, especially Beijing with the Olympics in 2008. I would try to visit the hutongs before they're all destroyed. However if your gf is at all squeamish you'll know that Chinese toilets are not for the faint hearted