First things first, for the sores, are you using chamois cream? I would highly recommend using chamois cream.
As for the shorts or bibs, if you have a gut, bibs are a godsend because there is no elastic waistband. I would imagine that it would be akin to either wearing suspenders or using a belt to keep your pants up.
I have two sets of pants/bibs:
1) The cheaper Castelli Duran bibs with the thinner and harder KISS3 chamois cause sores after an hour of riding but are okay for 2-3 hours with chamois cream. This is the same case for the cheaper Castelli Nero shorts.
2) The more expensive Castelli Endurance and Body Paint bibs with the better Progetto X2 chamois can go indefinitely with chamois cream (6 hours is my longest ride thus far). My more expensive Giordana FRC shorts with the Cirro Omniform chamois were okay for a three hour ride but the waist band dug into my gut. Since then, I got a pair of the more expensive Giordana FRC bibs with the Cirro Omniform chamois and have only ridden them with chamois cream.
Shorts or bibs, up to you. I think bibs are more comfortable but make sure you pay attention to the strap material because those can also dig into your shoulders. The importance of the chamois pad is obvious.
So, back to chamois cream - highly recommended.
Mark