Great topic.
My experience with juice buckets has been, first, that they are inconsistent. I have had Cabernet Sauvignon from Chile that was great one year and so-so the next year. I have had Zinfandel from California where one year it looked like White Zinfandel (it was only pink in color) and the next year had the rich dark color to which I am accustomed. Whites seem to be more consistent than reds so the issue may be one of incomplete or too short a maceration period.
One the subject of white wine from juice buckets, I fee they are the best (most economical alternative) because they emulate the process of making wine from grapes very closely. That is, the grapes are crushed and pressed into juice (without maceration) so buying a bucket of white juice is just like being at the winery.
One conclusion that I have reached in working with buckets of red juice is that I should always use either a grape pack or raisins in making the wine to add body, color and taste. I do like the economy of making wine from juice buckets but I feel I need to tweak them so that some of the apparent saving is reduced.
So, getting to the original question, my experience has been that as far as consistency and quality of juice buckets from various countries, I would rank them: 1. Italy, 2. US, 3. Chile.
As far as favorite variety I like the white juice buckets best: Pinot Grigio, Sauvignon Blanc. I have had good Sangiovese and Barolo from Italy, good Cabernet Sauvignon from California and good Carmenere from Chile.