Which is my real data usage?

I would say the one from the AT&T app

 

Top photo indicates lifetime usage if I'm not mistaken.

Bottom photo indicates the amount of data used in your current billing cycle.

 

The AT&T app matches what shows on my bill.

 

Did you restore from backup? It just looks weird cause it says you have been on the phone for over 3 of the last 14 days. That would be an expensive plan. It looks like you never reset it when you got your phone.

 

Believe it or not, that puts you in the "power user" category. You know, the people AT&T keep saying are ruining the party for everyone else.

Don't worry, so am I

I figure, the harder we power users push, the more likely AT&T is to increase throughput ability on their network to meet demands.

I pity the fool on a tiered data iphone plan

 

So it is just showing you the usage from your old phone. If you reset the usage statistics what the phone says will be closer to what AT&T says.
You should be able to look at the bar graph on AT&T's site to determine what your usage has been in previous months. If you never go above 200 MB then you can probably get a cheaper plan. You may want to decide if it is worth constantly checking your data usage and checking WiFi availability before getting a 200 MB plan.
If you are closer to 2 GB some months then you may want to stay unlimited. You may also want to consider what you will use the phone for in the future (video streaming/calling over 3G, or using MyWi) before giving up the unlimited plan.

 

In my first month with my iPhone 4 (not restored) it showed 10GB down. According to AT&T I actually used 1.8GB. I don't think 10GB would be accurate even if you included WiFi data. There must be a bug somewhere.
BTW - in the second month the numbers seemed pretty close to AT&T's figures. Maybe 4.01 fix something?

 

in the phone you have to reset the statistics when needed to have them show correctly...

I would go with the AT&T app since they are the ones charging you the $$$...

I think the data usage on the AT&T app takes more than a day to reflect the use of the day before (I'm saying this since I see 3days stat on your iphone settings usage).

Check your monthly bills and see how much you actually used at the end of the month not in between or 3 days later that is too short a time.... in-between month check is for people that might be scared of passing their monthly limit not for deciding a new plan....