What is the best male designer underwear?
No such thing! Whatever you feel best in. Naturally it is not the 5 pack from the local department store or you would not be reading this. You can have the play safe always OK option of Calvim Klein, etc. but this is so common in the meantime it really does not stand out as an expression of you. But basically the answer I believe is what you feel comfortable in, what you feel comfortable being seen it.
For me it is a compromise between quality and price (what else). Gucci boxers at $350 a shot are great, I admit, but simply not in my budget. I have chosen makes like Croota simply because the quality is great for the [rice you pay. Great colours, original designs, new additions to their range very couple of months.