My wife has a Kendal - We took it on our last road trip vacation. The advantage of 3G over wi fi is you can down load books on the run - we were in the middle of know where and she could down load a new book
With Wi-Fi you need to be near a router. Either your wireless router at home or a public one.
3G as I understand it uses cell phone towers.
I would pay the extra $50 is you expect to travel with the Kendal
We did not have to get an account with anyone. It came with the Kindle