I've been testing out undies. Bought a pair of Patagonia, ExOfficio and Terramar cool max bikini style undies. I've been wearing and laundering these through multiple wash cycles to make sure they will last through a camino. For comfort, I really like the Patagonia the best. Waist band is woven fabric and not elastic. Very comfy. I purchased the Patagonia at REI and they were $20 USD. Almost as comfortable are the Ex Officio. These have an elastic waist band but it is fine and doesn't cut or bind. The ExOfficio were purchased from Sierra Trading Post for $8.25. The Terramar undies for me didn't work out. The elastic waist band was uncomfortable, stiff, not stretchy enough and the stitching of elastic to fabric doesn't not look like it will hold up well. The Terramar were purchased from Sierra Trading Post for $6.25. For wicking performance all three brands did this well and were nice and cool.
Sierra Trading Post is a mail order discount outdoor wear supplier. They have good prices and the ExOfficio and Terramar undies would probably have cost more at REI. Since purchasing the first pairs, I'm really sold on the ExOfficio based on the cost and performance and am switching to these for every day wear, at home as I really like them and the price is reasonable.
If you shop the Sierra Trading Post website made sure you sign up for their sale emails. They will send you emails with links to purchase the items at a discounted price and sometimes offer free shipping. They carry Smart Wool, Ice Breaker, and lots of brands that are useful for your Camino.
I'm female so I was evaluating womens bikini style undies. Not sure how this info translates into mens undies by those three manufacturers. Maybe someone can do a side-by-side evaluation of the mens undies.
Laura