Pouch briefs changed my life. There was a point that I couldn't go anywhere without a bottle of good powder. Extra cans in every bag, vehicle, and bathroom. After making the switch to David Archy pouch briefs, I haven't used powder since. No more junk sticking together, no more uncomfort.
Sizing: Personally, I would error on the side of buying a little smaller, so they fit tight. You want them snug, so everything stays in place.
After my 5th purchase, I'm going to stick with the longer version as well. They help to avoid riding up or chafing your inner thighs when doing anything active.
Tip: Always air dry them. After 4 years, the first pairs purchased are still useable, with only small holes in the crotch. A dryer will break down all types if elastic.