Probably not what most mustachian's would recommend, but I use strictly Smartwool Merino 150 Micro Stripe Boxer Brief. At $45/pair they aren't cheap, but for me they are FAR worth the money.
I have been traveling for 17 months, carrying 2 pairs with me as my sole underwear. I've lived out of a backpack for over 6 months while the remaining was out of my car. I returned to Seattle to work and picked up my third pair at REI on sale. They haven't worn out, nor have they had any odor issues. I am able to wear them multiple days on end without having issues(up to 6 days a week before I wash them). Each person is different, but after the day's over, hang them up, let them "air dry" so bacteria can't negatively affect them(odor wise).
I also have switched to merino wool shirts and socks for the exact reason. Sure I have $500-$800 in merino clothing over 8-12 items, but considering that is all my wardrobe is and they have lasted 17+ months now, I am never going back to cotton.