Although there were many different successful shooter designs this year, I think the best ROI was in the hooded flywheel shooter, which was why it was so prevalent. Here's why:
1) Hooded flywheel shooters are space efficient over other wheeled shooters because they use less wheels, and if you design for it, the hood can pop down under the low bar (saw a few teams do this).
2) Hooded flywheel shooters are relatively easy to test/tune. Most catapult designs require mechanical tweaks to adjust power and speed. As long as your shooter wheels are overpowered, you can tune them down with encoders until you get the desired effect.
3) Hooded flywheel shooters put a backspin on your ball. Due to aerodynamics that I don't exactly understand, this means that the ball goes further, but it also means that if you hit the top of the goal, the ball has a high probability of rolling in. (hitting the top of the goal is far more common than the bottom because the robots are shooting up at the goal from below.
4) Hooded flywheel shooters are relatively easy to design. The only moving components are a single axle with wheels on it. No potential energy storing devices are necessary. Most teams have also tried this kind of shooter at some point in their history.
5) While both catapults and wheeled shooters can get worn down. Wheel wear is clearly visible, while springs or surgical tubing getting stretched is not as easy to spot.
I'm not saying necessarily that hooded flywheel shooter is objectively the best (because each design has its own merits). I am saying that the hooded flywheel shooter gives the best ratio of time spent (designing, building, tuning) to effectiveness.