I still don't get why it seems odd to go commando. You don't wear undies with a swimming suit, do you? Besides, pantyline is so unbecoming.

As far as "bad chamois" are concerned, a couple things I've learned over the years.

*The original PI 3D chamois: it grabbed "stuff" and held on for dear life during a road ride BUT it works great mountain biking. Who knew?
*The saddle/chamois/body position combo is critical. Sometimes they just don't like each other, but another chamois may love your saddle or may be fabulous in a time trial position and not on a mtbike.
*Flat stitching in your shorts is worth the extra cost. Sometimes it isn't the chamois or the saddle that is causing the pain.
*Thin chamois: Sometimes you can feel the seams in the crotch or on your saddle. When chamois wear thin and you can feel the seams on a road ride, the chamois may still be fine for mtbing because you move around so much more. A thin chamois also reduces chamois suck on technical terrain but can be incredibly awful on a century ride.

Moral of the story, don't assume a single experience with one chamois and with/without undies is the final solution. Experiment a little. I was about to throw out my PI 3D shorts because they were so painful for road rides but just wore them for 27 miles of singletrack. They were great.