Rule of Thumb - you will normally find the “best” cup of coffee at a speciality coffee shop or neighborhood roaster. This is their livelihood.
Quality of the outlets you mentioned vary considerably due to the specific coffee programs and emphasis the ownership or franchise places on their coffee program.
Wawa (not WaWa) places their coffee program as a point of differentiation over other c-store chains. Their coffee program tends to be one of the better c-store programs. Southland (7-Eleven) program is more cost driven and less consistent among their stores.
MCD has a good quality (McCafe) program if the individual franchisee runs the program properly. BK has an extremely poor program.
Diners - in the NYC/Phila area tend to use average to below average (Greek mafia) coffee. Make sure they replace the pots every 30 minutes (if on a burner). I love when they take the last third of a burnt pot and top off the fresh pot being brewed.