There are some things to decide before you can choose the motor:
- race or cinematographic (a race drone needs a higher KV than a cinematographic one)
- the propeller (look also to the KV, this needs to be the same as the motor)
- the ESC (the electronic speed controller is also connected to a class of motors, look to the current)
- the battery (this is more linked to the ESC, but look for this to the amount of cells)
And everything else is just personal preference. It is possible I forgot something, but these are the most important things to look out for, I think.