RW-8 if you have sand, RW-15 if you run BB.
RW-15 moves a lot of water. I know it's rated for "only" ~3100GPH, but at full speed it moves dramatically more water by volume than a Tunze 6105. When positioned ~6" below the surface and pointed directly at the opposing wall of my 120, it moves more water in a gyre motion (towards the opposite wall in the top 1/2 of the tank, towards the pump in the bottom 1/2 of the tank) than two 6095s running at 100%. Extremely wide flow. A Tunze (or the WP series Jebao pumps) generate an extremely high velocity stream. The RW pumps create flow that's more akin to a moving wall of water, more like what you feel in an ocean current.
At full tilt ~4" below the surface it generates enough flow to create vortices that pull down air on the opposite side of a 4' 120. In a 40b it will generate strong enough vortices against the far wall to pull bubbles halfway across the bottom back towards it.
I've decided to move my 4 tunze pumps (6105, 3x 6095) down to the 93 cube I'm setting up as a dedicated 'nem tank, because two RW-15s can move far more of the tank's volume with a more desirable flow pattern than the 4 combined.
That said, I do have two complaints. In "C" mode, the dials on the two pumps to determine how long they run do not exactly match. When the knob is pointed straight up, both pumps should alternate on/off roughly every 30s. They don't match perfectly. One of them is also slightly noisy. Quieter than a Vortech, but I value my silence. If it doesn't quiet down after a little more run in time, I'll get in touch with Reef Breeders.