high power vs low power dc motors
The biggest differance comparing the datasheets you provided would be the Current they can take and the speed/power it can generate. Now in your case I believe it depends on the speed/power/etc of the application you are using.

The key is in here:


  Key specs at 6 V: 280 RPM and 550 mA (max) free-run, 90 oz-in (6.5 kg-cm) and 6.5 A stall.
  
  Key specs at 6 V: 170 RPM and 250 mA (max) free-run, 50 oz-in (3.5 kg-cm) and 2.4 A stall.


Now which one you would get depends on the speed you need/etc which are written in the key statements shown above. That is as much info I can extract without additional information on your application.