With the current Assos bibs (the ones with the blue chamois) it is my experience that whether they are comfortable or not is dependent on body shape. I have narrow sit bones and I find that they ride up and cause chaffing (this is, I think, caused by the fact that the chamois is only sewn onto the shorts around the edge - I have made a couple of pairs wearable by hand sewing the chamois to the shorts down the middle bit of the chamois). Others I know with wider sit bones reckon they're great - although you have to get the sizing exactly right (too big and you are asking for trouble).
For me the best chamois I know is the Castelli Progetto X2 - but the shorts themselves are not as well made as others (and the sizing is very small). I have also had good success with the higher quality shorts from Giordana, Santini and Pearl Izumi. My all time favourites are Gore Xenons and Rapha Classics.