Also, this decision should be based on what body areas are your strength's or weaknesses or what you want.
I know symmetry is important, but I also know my wife loves Shoulders. I want to be able to totally blow out my Shoulders, and to do that I want them done by themselves and as rested as possible. Hence,
Chest/Tri
Back/Bi
Abs Cardio Rest
Legs
Shoulders YEA !!! .
Weekend Rest
Also, some of us have a 4-5 day splits because our weekends are too busy to get to the gym.