To me, the lack of simultaneous voice and data is a deal breaker. Sure I've used it for little things here and there, like helping someone on the phone with directions or reservations on OpenTable while talking with my wife, but it's become a critical feature for me.
Traveling frequently for work often forces me to run my business from locations without wifi and I find myself constantly on the phone with clients or colleagues where I'll need to reference emails they are sending live in real time or retrieve specific data online during the call. This often happens multiple times a day and I simply could not operate without simultaneous voice and data. It would kill my productivity and make me look unreliable and inefficient. So for those that make blanket statements that it isn't needed and is just a luxury you can work around not having it, that absolutely is not true for many of us.
More broadly, why can't we just be happy that we now have choices as to which network we'd like to use our iPhones on instead of in-fighting about it? Why does it always have to be a competition? Sure, each has their advantages and you can choose now where you'd like to send your monthly cell payment, so why bash each other? Does it make a bit of difference to you personally if I am on AT&T and happy with it? Does one's choice in cell phone provider make them a better person?
It's a shame when you can only elevate your status by stepping on top of someone else.
Save the fighting for bashing this Fandroid people instead!
(That's a joke, BTW!)