I only use bags. Never racks. Over the last 10+ years my fall/winter/spring evolution has been:
chrome metropolis
bagaboo workhorse xl with extra strap
trashbags garbage truck
in the summer I’m all about that Ortlieb backpack. The closed cell ventilations pads are the winner. The Commuter line with no padding in the straps soaks up no sweat. I also recently got the Ortlieb messenger backpack for bigger summer loads and it’s great too. Although I’m not a fan of the velcro closure. The hook on the commuter is much better.