Metomeya,
New York - Unless you have the fundamentals of a GQ model, Manhattan is a lost cause. Every 1 out of 2 girls are gorgeous, but you won't get much time of day to make an impression. I'd guess you'd need to be a little more high energy here. Outside of Manhattan is much easier...but the ratio of attractive girls is also lower.
Las Vegas - I don't really have much to say here. On my second approach in LV, I got the instant lay with probably the most attractive girl I've been with. Of course, that's also a lot of luck, so I can't really give an objective opinion. But the atmosphere in LV in general is really open; most people will be very honest with you. It's a little refreshing, actually.
LA - The amount of attractive girls in general in Cali are ridiculous. LA, specifically, is alright. I'd say it'd be better to go to San Diego, that place was a goldmine. Santa Barbara was also pretty fantastic (had a good time at UCSB

).
The thing about gaming in the States is that you shouldn't pass up an opportunity to be in a more rural area if you can. No more than a few days, perhaps, but girls out there will be similarly attractive with guys who have poor fundamentals. If you're wearing a casual shirt (button up), and nice shoes, it'll do you a good deal of great here.
Nick