JamesBlue saidWhat proportion of your chest routine is pec flys versus chest presses?
For you does it differ according to which part of your chest you currently want to build?
All parts of the chest should always be hit, not specific portions. On chest day, it's important to hit all angles so that there's balanced development. A major issue for lots of guys is commonly chest pressing, and developing heavily at the bottom, but don't have an upper chest (incline press) or the dividing crease between the pecs (flys).
So do them all! Just pic diff variations of the movement to change it up.