iPad Wi-Fi Only for me.
Before the iPhone 6 Plus was introduced, I was seriously considering getting a cellular iPad. I'm not in a lot of situations where I carry my iPad beyond the house, except for travel. The few times where I am on extended travel and would prefer a larger screen prior to getting to a hotel with free WiFi was just enough to justify the expense.
Now the 6 Plus (and the carrier switch) is filling that gap for me. I have a screen large enough for navigation, surfing, etc. while in motion. The iPad will work for being stationary. Saving on the cellular bill too.