I have done all three and I'd rate them backpack, trunk bag, pannier in terms of pure performance. That being said, the backpack has to be a good cycling specific one and not overly large (more than 20L). I just started using a Dueter Air EXP and it's great for my commute. My issue is that I like to switch bikes too often and having racks on all of them is just too much of a pain. The Dueter distributes the load well and keeps your back from sweating.

My trunk bag also works great, but other than having to have a rack for each bike, it puts the load up too high and makes for some funky handling. Aerodynamically it doesn't seem to hold me back though.

Panniers do get the load off your back and down low, but handling is still affected and aero drag goes way up.

10 mile commute each way, only carry clothes (no shoes) and lunch.