I almost always use panniers. I started my bike commuting years ago using just a backpack. On my long commute, it was just too uncomfortable with heavy loads, which are not uncommon for me since I do ferry supplies/clothes to and from work but still just about never do it using a car. Tried the rack and panniers and haven't looked back. I might still use a messenger bag or backpack for short commutes around where I live. I do miss how the bike handles unburdened with panniers. Ever try to bunny hop with loaded down panniers? It's not pretty.