They're both very good - I get the USA ones as I like to be able to reverse them if needed, and because of the small additional weight saving.
But I wouldn't bother getting the USA if a bass already had the Korean ones on it.
I do wish the string posts were slightly tapered to force the string to the bottom, but I can't have everything.
BTW - the Y key ones are a little lighter than the clovers, with the lollipop in the middle. I believe the Y keys are the lightest tuner ever, but for clovers the Sandberg lightweight tuner is a little lighter. The Sandbergs are a real pain to get in the UK though as their online shop currently won't ship out of the EU.