I guess its just a matter of personal preference. I like shooting the top barrel first. Most of my shooting is done on wild birds over my dogs.I have ejectors but don't use them as I don't like littering my hunting area with empty's.
I like to reload without looking at my breech and keeping an eye on my dogs and where the bird may have dropped or disappeared to.
The top barrel just seems to work best for me.
When I shoot dove many times I shoot the bottom barrel first just to even out the wear. Then again when I shoot dove I use the ejectors and eject most spent rounds into a 5 gallon bucket. Im not roaming around so those that miss the bucket get picked up when Im done shooting.