I mostly look at the schedule for things I want to do. For my upcoming trip, I'm starting at DL in the morning on the days that Tale of the Lion King is showing because I may want to see the 12:30 show. The cavalcade is now later in the day but when it was before 1PM, that could have been a deciding factor. But with the current timing, it makes it impossible to start in DL, do the DCA Visa photo opportunity and see the first cavalcade in the same day so I'd favor starting in DCA when Tale of the Lion King is not a factor.
When there are food booths at DCA such as for Lunar New Year, that could have been a reason to start there instead. At 1PM, crowds flood that park for the food.
The other factor is what rides I want to do in the morning. Before Early Entry was introduced, Midway Mania lines were short in the first hour of park opening making it possible to grind the ride a few times so I favored DCA start.