Have heard both that it doesn't matter which ones to get and to only get the US made versions and stay away from the imports.
I notice that most companies only have one uca and don't mention whether its US made or an import.
I always get my suspension pieces, UCAs included, from American Pony....the US counterpart of Canadian Mustang. They sell the 4 rivet arms that are still manufactured by one of the OEM suppliers that made them for Ford almost 40 years ago.