I like to wear U.S.N. Swimmer shorts, the down side is there is nothing to keep the jews from peeking out the leg holes.
I recomend a company out of Santa Barbara, CA called Aeroskins. They make shorts and swim wear out of polypropolene which has a slight thermal property and dries out fast after a dive. My only pair has sadly lost their waist elasticity.
Seriously, working divers and those of us that do serious research diving don't wear anything under the wet suit. It is more comfortable, less stiff to wash later and the wet suit will have less free space in it for water to circulate through.
I just read the post by JessH, commercial divers in the Gulf of Mexico where the water is 70 to 80 in the summer wear jeans as their wet suit to go to work at depth. Saves on buying an expensive neoprene suit and trae it up on barnicles.