I'm a very light sleeper, so Flying J's were a poor option for us. The first time we stayed at one, the noise from the reefer running on the trailer next to us was annoyingly loud (we were in the RV parking lanes - it was some sort of enclosed car trailer); and then the second time, we parked on the "quiet side" of the restaurant only to be treated to a drunken, screaming-obscenities fight in the parking lot at 2 AM.... that's when I said "Never again".
We're generally not in so much of a hurry that we can't find some RV park to stay in; or if we are, we'll opt for a Walmart or Cabelas...