wow thats a tough question. I can't tell you exactly but here are my top guesses:
1. EA Sports NHL series (I've owned 98-01, 03-07, and 09) - 10 games in total
2. Call of Duty (I've owned Finest Hour and Modern Warfare, plus playing CoD3 and WaW) - I played Modern Warfare a ton
3. Gran Turismo (I've owned 2, 3, and 4, plus playing GT5:P) - I played them all a ton except for Prologue
4. Need For Speed (I've owned approximately 4 or 5 of them in total, plus I've played most of them at least once, a longshot though)