IDC ribbon connectors I normally use a vice. I have used pliers and mole grips in the past, but it's better if you can get the whole connector to crimp square and at once, with control over how quickly the connector closes.

Boyan, those crimping pliers won't cover that many connectors. I've got a set with 12 interchangeable jaws, and it still doesn't cover everything I need it to. I spent most of my life dealing with vehicle electrics, and some terminals just won't work without the correct crimping jaws. And although soldering will work, as I said in my previous post, you risk the wire fatiguing and breaking, especially if it's done poorly.
Unless the connector is designed to be soldered, I would never personally solder it.
Best case scenario if a crimp/solder joint/wire fails, is things stop working. Worst case is the drive and/or motor gets destroyed.
Ultimately how well any method will work, will depend on the final implementation. A cable that is well secured with minimal vibration, doesn't have the same risk of failure as something being constantly vibrated and flexed.