I just got these things last night and am pretty sure I'm never going to take them off. Although to any ladies out there that are reading this, yes I do change my clothing on a regular basis. That being said, these are probably the most comfortable boxer briefs I've ever worn. Some other people had said that there was a problem with a bit too much sag in the *ahem* crotchal region. I actually have not noticed this at all.
For sizing reference: I'm about 6'2", 6'3" on a good day, and about 170 lbs. I ordered a medium and they seem to fit great. They are definitely somewhat long in the legs but because they are nice and snug they don't ride up and bunch up as some other boxer briefs I've had. If you're on the fence about sizing go with the smaller of the two options you're thinking since they are a nice, somewhat stretchy material.