Small waves the last days, I thus experimented a lot of fin configuration... it just takes 30 seconds to change the fin setup on the spot (be careful not to drop the fin, they sink).
I am more and more found of the MR (Mark Richard) Twin fins for small wave conditions. By storing some trailers in the wetsuit (chest zip suits also are very practical to store fins in the pouch above the zip), or maybe a fanny pack, it is really interesting to compare different setups on the same spot at only minutes of interval.
I thus tested on my modern 9'3"x27" longSUP (Gong Moblog):
Only the twins: fast and loose, but can lack drive at the end of turns

Small rear fin (or a big trailer): one of the rears of the Gerry Lopez quad set: the reliable feel of the thruster with the added speed and playfulness of the twin

Quad version: smoother ride than a pure quad (rears have symmetrical profiles, and the boxes are close to the stringer), good for fast sections

The full MR set: twins + trailer. A very good compromise, most of the twin playfulness and speed with just enough drive

And last, my favorite setup for the day: asymmetrical setup with the trailer on the frontside (I am regular) for mostly frontside fast waves: faster than a thruster, good traction for max speed on fast sections, but no need to get too much on the tail for rollers and cutbacks so I wasn't killing all my speed on these small waves (waist high)