My humble opinion on this.
SY42STH47-1504A
Inductance too high (4.8mH) the motor's torque will quickly decrease with rotary speed (rpm).
17HS8401
The inductance is still not the lowest, but pretty acceptable (3.2mH). It's actualy what I choose for my machines, but for the last 10 motors I bought, 1 was not acceptable, it does not spin properly. So check well when you recieve your motors.
For lazy people : the lenght of the motor is linked with available torque, your required torque depends of the efforts the motor will hold. Then look at the inductance, the lower, the better.
The choice of the motor is the result of a calculation for a specific situation. I won't explain the calculation procedure here. A lot of manufacturers give
stepper motors selection guides. (It's easy if you try). So all depends of the machine itself and of what is expected. My advice, don't ask for someone to do your shopping, ask for knowledge (or where to get it). Get some skills.
Collective intelligence emerges when a group of people work together effectively.
Prusa i3 Folger (A lot of the parts are wrong, boring !)