Exofficio Give-n-Go boxer briefs. Almost every thru hikers wheres them. I now wear them to run and lift weights in. They're awesome. Just look at the reviews on Amazon
https://www.amazon.com/ExOfficio-Mens-Give-N-Go-Boxer-Brief/dp/B001M0MN16
I use the 9" version
Ex OFficio Boxer Briefs. They're synthetic fabric and dry quickly and without smelling terrible. For example, I went to a week-long martial arts camp with several workouts per day and no chance to do any formal laundry; I wore these (separate pair to each workout in a day) and just rinsed them in the shower after my workouts, and they were not smelly even after a week's worth of workouts.
They're not super sexy, but they're super functional, and worth every dollar I spent.
Ex Officio boxer briefs are wonderful - they're comfy, they don't get smelly super easy, they're a wonder to work out in. They're probably not as sexy as some of the other suggestions here, but they're not unflattering, and they're good underwear.
Just came back from camping in Zion, with heavy hiking. I wore one pair of Ex-officio boxer briefs the entire time: http://www.amazon.com/ExOfficio-Mens-Give-N-Go-Boxer-Brief/dp/B001M0MN16/ref=pd_sim_sg_1?ie=UTF8&refRID=08DW6FWEQ54XXWJH55E2
No smell. No discomfort. You might want to get two pairs just in case you shit all over one (traveling to new places with different food practices can sometimes be rough).
You might want to look into smartwool products for your base layer tees. I sweated the hell out of one of their shirts during the day and slept in another at night. Again, no issues with smell.
But yeah, your base layers -- the stuff you'll wear the most often -- should be wool or some sort of technical fabric that dries quickly, retains heat when wet, is light weight, and doesn't stink. Most of my research when looking into gear that fit this description directed me towards wool, though I was surprised with Ex-Officio.
You might also want to x-post this to /r/backpacking
I wear Exofficio Men's Give-n-Go, a little bit on the expensive side of things, but they are comfy to wear.
in case anyone was wondering it's exoffico boxers
What are they?
Edit: Found it.
Ex Officio is the brand, "GiveNGo" is their name. These right here. All I wear.
>I really don't know why men can't buy underwear that is exactly the same cut and style as normal underwear, but made of satin or silk or other exotic material. it's a shame. . . . boxers don't count, because lots of boxers are made of nice slinky shit.
I think the reason boxers get made with nicer materials is because that they are much more popular. As far as awesome underwear goes thoe, may I suggest ex-offico boxer-briefs