[Nemo]

Factors favoring single speeds:

1) You might be able to use a one stage gearbox instead of a 2-3 stage to get better efficiency. That gives you the same benefits as using more powerful motors, except you don't have to draw the extra current and produce the extra heat.

2) Single stage gearboxes are lighter by a pound or more.

3) Pneumatics weigh several pounds, so you have significant weight savings available if you're not using pneumatics for anything other than shifting.

4) Single speed boxes are thinner, and you could have certain situations where that becomes important. For example, you can fit a battery between the CIM motors sometimes, but using thicker gearboxes could eliminate that possibility depending on the setup.

5) Cost is a factor, of course, but consider that it's even more of a factor if you're on the edge of being able to make a practice robot. Now that components are cheaper, more teams will hopefully look at practice robots. When you have to buy four of every transmission, the $110+ difference between single and double speeds turns into $440+, which is a decent chunk of your second robot.

6) It's easier to make a custom single speed transmission than a custom two speed transmission. That has benefits, but the one that I'll mention is that you can more easily make a direct drive robot with a custom gearbox that mounts to your frame in some convenient way of your choice. Direct drive can increase your reliability and decrease complexity. It can also make it possible to drop another reduction stage (see item #1).