Bibs. They don't slide down so there is never any "plumber's butt." Since no waistband is needed to keep them up (more or less), they are less constricting in the waist.
The downside is that bathroom breaks are more complicated, especially going #2, but that really is not an issue on most rides and is a small price to pay for better function and comfort.
tiger1964 Just get some clip-on suspenders for your shorts. That works pretty well. I use this solution for my tights.