The GPS version allows you track your location which is really good if you run a lot because it helps accurately track your distance as opposed to using haptic features (basically vibration to estimate how many steps you've taken).
The Verizon option lets you purchase a cell phone plan for your watch so that you can use text, phone call, and web features without being connected to your phone.
I personally just get the basic version because it tracks your steps and calories pretty well and if you want to view text messages, twitter, facebook, Instagram etc. all you have to do is connect with bluetooth to your phone and make sure your phone is close by (like in your pocket or gym bag). I dont really see the need for the option that allows you to get a cell plan unless you leave your phone elsewhere a lot.
Cheapest price = basic watch
mid price = GPS added
high price = GPS + cell/data plan added (and remember you pay monthly for that plan also)