I try not to wear shorts with a built-in brief as the elasticated edges of the brief can be really variable in quality and I've had some bad chafing after a few hours running. Also, for trail runs over two hours I wear a Salomon S-Lab belt and it tends to wick sweat from my shirt to my shorts, so everything is soaked. Compression shorts help; I use Nike or Under Armour. I have just got some Arc'teryx shorts with a brief (despite what I said above!) and they were great during their inaugural run (35km trail run in 30°C heat). Im going to try the Salomon S-Lab 2-in-1 shorts, which I've seen at 40% discount. Full retail for those shorts makes your eyes water more than a nasty case of chafing!