I currently have a Droid X on Verizon and will be switching to the iPhone shortly. However, I haven't decided whether to get the Verizon iPhone or go back to AT&T...
IF the Verizon data plan is still unlimited at the current price, AND if the Personal Hotspot feature is included at no extra charge, it will be a no-brainer for me and I'll certainly get the iPhone on Verizon.
I don't think the hotspot feature will be free, however, so if that's the case then I'm just not really sure which to get. If I go with AT&T, I would gain simultaneous voice/data and have faster speeds. However, if I get the Verizon iPhone, I should have more consistency.
I think right now, there are just too many questions. We don't know the data pricing yet. We don't know for sure it will be unlimited data. We don't know if the personal hotspot is free or priced the same as Verizon's other hotspot phone offerings.
And there's the more long term concerns! We don't know what effect the influx of iPhones will do to Verizon's network. We don't know whether the antenna will be improved on the Verizon iPhone. We don't know whether Verizon will get the iPhone 5 this summer at the same time as AT&T.
The smart thing to do is just wait it out before jumping in. However, I plan on buying my iPhone 4 off-contract and will use my upgrade pricing on the iPhone 5. So it really doesn't matter which one I get because I'll be selling it in June anyway (unless Verizon doesn't get the iPhone 5 until later).
Too many questions!