The Wi-Fi is the most popular one due to its been available longer and it’s cheaper but to answer your question – yes as long as you have a Wi-Fi connection. Of course you can watch movies, play games, listen to music and read books without being connected.
You can use your phone as a hot spot if you are inclined. I have heard stories of people who have jail-broken their iPhones and just connect their iPads to the iPhone but I wouldn't really know
If I had to do it again – I think I would buy the 3g and for the added functionality of the 3g as you can buy months as needed so there is no contract.
If you get one - make sure you have an Wireless N supported router and its blazing fast!!!!!
If you get one - it just might change how you do things!!!!!
It all depends on what you want to do