Quads would have more fin in the water just because of fin placement. Some of the pro surfers have switched to quad set ups for really hollow breaks like Teapu but like most things it's a personal feel. Use both set ups and go with the one you feel most comfortable with.
Try both. Quads have more grip and more speed when driven hard in fast seections Thrusters allow for more control and precise positioning in the wave, but can slide a little if you are not well committed in turns.
And hybrids are also interesting: - quad + nubster - quad + trailer fin (the small ones used in the Twin fins + trailer setups) , my favorite for heavy conditions - thruster + "bonzer" quad rears - "mock bonzer" setup: bigger center fin + 4 bonzer mini "keel" fins - ...
My 8'4" feels easier to get up on the rail as a thruster, especially in the juice. It has a fairly flat bottom, not a great deal of V and very subtle concaves.
