I wanted to start this exact thread earlier today! Okay, I usually use Ortlieb panniers but it's kind of a PITA to load it up with whatever I need each time and attach it to the rack, then ride wherever I'm going, unload it and carry the pannier awkwardly all day. Panniers are great when I have huge, unexpected loads like groceries or laundry but that's not that often and I think the weight of the rack affects the ride too much. I just don't carry enough on a daily basis to justify having a 3 pound rack attached at all times. So I bought an Ortlieb Tracker 35L which expands to a pretty huge size and I'm gonna take off the rack, so I can carry the backpack easily with me when I need to carry a lot of things or leave it at home and enjoy a more lively ride. So both are good but panniers really shine when you have a huge load to carry. For my daily needs, a backpack with the ability to carry a lot more will do.