Been off the board for a while. back now! JUN pistons are made by Cosworth, here in the UK, but they will not, at all, never, ever sell direct. We buy a lot of stuff from Cosworth, they wouldn't entertain it, I know people who spend hundreds of thousands with them, they too couldn't get them direct. Honourrable comapny! PITA
My limited experience of HKS ones is they work OK, but are very heavy. Skyline 2.6 GTR ones a considerably heavier than stock Nissan ones, and i have never had a definitive answer from HKS as to whether they are forged or cast. they look cast to me... The Skyline ones didn't have the stock oil cooled head galleries either, which added weight, MAYBE added strength, but seriously reduced ring land and piston crown heat transference.
If I end up doing this 1JZ-GTE engine it will have Cossie pistons. Full stop. They are the best, and worth the price hike via JUN, IMO.