For the first three weeks I was using the bumper case. I like the bumper, but, after 20 months being carried around in my pocket, my Droid 3 had dust in the headphone jack, USB port, HDMI port, and even within the removal back. Everything still worked fine, but I knew this would continue to be an issue.
So, last night I went into VZW and bought the Otterbox Commuter case, which has port covers for the headphone jack and USB port. It makes a phone that's already a little on the big side even bigger, [edit - and a phone on the heavy side even heavier], but I think not terribly so, so I am going to try this out for a while.
I may go back to the bumper case, though. We'll see.