For what it's worth. I take both off. I drain the bike with the main drain plug on the bottom of the motor, and then I remove the filter screen cap. Why?
The reasons is pretty simple. I have found that by doing just one, there is always a small level of oil and particulate trapped in the sump. I wanted to ensure that I got as much old oil and particulate out as possible. I also tend to leave both open and run maybe a quarter to half a quart of clean oil through with them both removed. I always have a little left over oil from my 4 quart jugs of rotella, so it works well for this.
Am I known for my overkill when it comes to maintenance? Yes. But, I am also known as the guy that daily drives 30-50 year old vehicles with nary a problem.
