I can't decide and they are all so expensive. Also, if anyone knows how to make one, please tell!
You can make one easily, using boxer briefs, a "O" ring and some sewing skills. It wont be as good as buying one already made but it will work if you're in a pinch! Just google how to make packing underwear, tumblr has a few great tutorials!
As for products, I highly recommend the trunks packer!