It's probably true that on avergage Japanese girls are prettier than their other asian cousins, however I do agree that Thailand and the Philipines are easier places if you're a European man after a "different" experience. If you're a first timer with an Asian lady, you'll really not notice the difference between Japanese and other Asian... they're all cute
If the op hasn't yet tried these places I would respectfully suggest that these countries are his first port of call. If you do your research and have your wits about you, there are many beautiful young women who are willing to make your holiday an experience of a lifetime, without you having to mortgage your house to pay for it.