Wasabi may be grown commercially exclusively in Japan, but is also grown on a small scale in Hawaii. I live in the Volcano area on the island of Hawaii at 4,000 ft. elevation where winter time temperatures can drop into the 40s F. The guy raising the wasabia japonica is also a commercial vegetable farmer. His wasabi plants are watered 4 times a day and he has harvested mature plants. He got the original plants from another Japanese farmer who imported them from Japan.
The first ingredient listed on a tube of PREMIUM S&B Wasabi Paste is wasabi. It sells for 3 to four times the price of the colored horseradish. As for preference, it depends on how much you want to spend.