The Pronto is awesome because it is cheap, while still carrying the bare essentials while being as small as possible. We toss this on the stroller all the time when we are just going for a short walk and we even put this inside our other bags when we go out. If you have some shoulder bags or backpacks that you love and you don't want to go all-in on a diaper bag, you could even just get a Pronto and use it to "convert" any other bag into a diaper bag.
I had a diaper bag all picked out for my May LO, but now that I've decided to get a ring sling I'm not sure it will work. I wanted a backpack diaper bag, but will that mess with the shoulder too much? What do you do for a diaper bag when babywearing?
While not exactly a diaper bag, the Pronto is an essential accessory to any of the diaper bags listed here. It's cheap, small, and has a great roll-out changing pad that is very easy to clean. It's got a zipped compartment for wipes and a netted pocket that is big enough to hold 2-3 diapers and an extra change of clothes.
I've used both with no issue - though neither was designed specifically as a diaper bag. My slight preference goes to a messenger-style bag that just goes on one shoulder.