I own all three of the shorts that you mentioned in your initial post. The Castelli YPro is a distant third, in my opinion. The chamois, is okay, but occassionally can chafe at the seams where the "wings" are sewn on. The worst thing about these bibs is the fit. The legs are okay, but the upper, around my waist and lower back, is loose and floppy. If I had gotten a smaller size (mine is a large, and I'm just over 6' tall), there is no way I could have gotten the legs over my thighs). Its as if the bibs were made for someone shaped like Spongebob Squarepants. I used to have a pair of Castelli "Dome" bibs, which were cheaper and preferable to the 2005 YPro bibs I have.

With regard to the Assos, I think its a toss-up between the Uno and the Mille. I actually think that the Mille chamois is slightly less comfortable, due to the extra padding, but it has better frontal coverage with the terry section in the front of the chamois. I've noticed that the saddle I'm using makes a difference. When I used to ride an Aliante, the Mille was preferable. Now that I'm riding a Toupe, I actually like the Uno chamois better. The Mille bibs might be better in the heat, due to the all mesh straps and the little inserts in the front of the legs, but I've never noticed either bib being hot. I basically decided to only buy Assos, as its my favorite with regard to fit and cut (though I've noticed that lately their jerseys have gotten cut a little looser/longer) and even when I only had one pair, I'd forego my other shorts to wear the Assos pair.