Are foreign girls better looking than American girls? Yes.
Are American girls better looking than foreign girls? Yes.
It just depends on the girl.
This is a little weird, but it's the best way I've got to describe my experience with overseas girls, in my case, Japan.
The girls in the US tend to follow what's called a bimodal distribution in terms of hotness. Between the obesity epidemic and the general trend towards thottery, there's a lot of really ugly girls, and a lot of really hot girls, and not a lot of average looking girls. If you were to rank every girl in the US on a 1-10 scale, and then put them all on a graph, you'd see it looks like this:
You see a lot of really obese girls who don't take care of themselves at all. Girls who look like this:
You also see a lot of really gorgeous women, who spend hours in the gym taking care of themselves, spend god knows how much money on cosmetics and surgery, and follow an absurdly strict diet. Girls who look like this:
Looks are clustered around the extremes. Lots of 8 and 9s, lots of 2s and 3s. Not a lot of 5s or 6s.
In Japan, at least, hotness tends to follow a normal distribution, which looks like this.
Most of the girls look about average. The majority of girls are about the same height, about the same weight, and have a roughly similar facial structure. They all look something like this, though she's a little prettier and has slightly nicer makeup and some photoshopping.
Very slim frames. Very little in the way of breasts. (Nicer asses than you might think, at least in my experience.) Not a lot of land whales, and not a lot of head turners. They're not going to blow your mind like the best American women, but they're not going to make you want to douse your eyes with bleach, either.
As for pleasantness, it's absolutely no contest. Last time I was in Japan I had to entertain some American chicks who were tourists from overseas. They were quite attractive, and they were nice enough in their way, but I remember dropping them off at the train station and saying to myself, "Good lord these girls are so self-centered..."
Japanese girls win, hands down. There's plenty of selfish, bitchy, drama-queen-ish Japanese girls, but you can just avoid those. It's not 100% of the entire sex like it is here in the US.