Just to the muddy the waters, we use the U.S. edition because we think that the US edition is more challenging. IMHO, the standards edition dilutes what is so great about the Singapore curriculum because it is designed to cover all of the same topics that the typical US curriculum tries to cover. Although I'm sure that it is still far superior to most US texts, I preferred to avoid the "Mile Wide but Inch Deep" problem.
YMMV, of course.
Have you actually used the Standards edition? I have compared 3B of the US and the Standards edition side by side and I can assure you that there has been no dilution. There are a few added topics and that is all.
We recently switched to the Standards edition because, of all things, my son prefers the color in the textbook. If anything, he is finding it more challenging. I like that the practice and review sets are distributed more evenly through the program.
