The cellular ipad has the GPS chip and the wifi only does not. This may be a factor in your decision. I got the cellular version for this reason and if I ever need to use the cellular connection, it is available for me.
If your mobile device (example, iPhone) has a GPS and you tether to your iPad, then the iPad will use the GPS information from your mobile device.
But once again, if your mobile device has the data connection and GPS then why do you need it on your iPad? I have a wifi iPad and I am always near by a wifi connection at work, home, with friends or local shops and for those rare moments that I am not I have my iPhone to look up information.