This is really going to depend on how and where you are using it. I bought the 32GB Wifi only and this is my first ever iPad. My reasons for choosing how I did:
1) I don't have AT&T or Verizon service and I'm not going to pay either of them just for service on my iPad.
2) 4G versions cost more than what I wanted to spend.
3) I will use mine mainly for web surfing, research, some business productivity, reading books, and the occasional times for entertainment (games, movie, etc) when I'm traveling via plane or car. Most places I go will have free Wifi even when I travel and I certainly have Wifi in my house.
4) The rare times I don't have Wifi access, I have my smartphone, which is what I have been using A LOT since I've had it. Just ready for what a tablet offers over a smartphone which is why I bought the iPad.
All I can say is think about what your needs are, what you can afford or are willing to spend, and go from there. Another thing I read here is that you can purchase a 4G model and not activate the service until you actually need it. That's a nice safety net to have also.