The problem with this concept is that I would normally carry five or six, so if i had to narrow it down to three, it would be drivers that may not necessarily make it into my normal, bigger rotation. With that being said, here are the three I wold carry:
178 Gold Line River. Stable enough for a level straight shot or mild turn over fairway shots. This disc would be used the most.
175 Champion Firebird. It can handle thumbers, hard anhyzer angles finishing flat, and head shots that need a strong finish.
170 Echo Star Boss. It has been beaten in enough to track right if I need it to but has enough stability to go anywhere I want for maximum distance.