How much data for an iPhone?

I want to buy an iPhone 5 within the next couple months but I have no idea on how much data to get. I'd prefer to get Verizon, however their plans are the most expensive. I'm thinking about the plan that has unlimited call/text and 1gb of data. I've never had an iPhone or smart phone before so I have no idea how much I'd use it. I'd mostly be using the data for twitter, facebook, email, and occasionally checking sports scores/instagram. However that plan is $90 while for that same price I could get 450 messages/unlimited text/3gb of data with AT&T. What's the quality in service difference between AT&T and Verizon? Would it be worth it to get the two extra gb of data from AT&T?

Why not start low, you can always raise it. If you watch alot of video then that consumes a ton, I rarely use 200 meg a month and I read stuff everyday on it, but no video.

ATT has the best coverage, in my area at least. And their data is the fastest.
The plan I picked when I picked my iPhone was 450 mins, 3gb of data, and unlimited texting which total out to be $90+tax per month. It's expensive, but what can you do:\ But since this is your first smartphone you might want to go with a lower data plan.although i didn't see an option for 1 or 2 gb for at&t, only 300 mb.