I'm gonna rank transmissions in a little list here. Keep in mind these are all my opinions and observances, so yeah.

1. Best! Your own custom tranny. You can build it to the weight, size, and everything that you want. It also gives you great control over your bot, as you can change everything to be what you want.

2. The upcoming (soon to be sold) transmissions from Trossen Robotics partnered with OutBack manufacturing. These are still in the design phase, but they'll be quite the system. Very robust and light, as well as decently cost effective.

3. AM shifters. I've never used these because my team keeps making me design and build my own, but I love these things! They're incredibly cost effective and robust for their weight. They're also proven, reliable, and an all around good system. They get the Craig Seal Of Approval.

4. Dewalts. These are a great budget tranny, but I'm not a fan of their robustness. People may brag about them being sturdy, but I've seen too many of them shatter. There's just a certain amount of structure you gain out of going with larger and non planetary systems. I'm not dissing these, I still think they're great. Personally, I would limit them to budget bots and Crab systems looking for multi speeds.