Well, I wish I didn't travel internationally so much after seeing the data rates both AT&T and Verizon are offering iPad users for monthly, non-contract plans. If you are deciding on whether to get a Verizon iPad or an AT&T one and will use 1 GB or less of data per month, Verizon just decided for you.
As you can see from the chart that AllThingsD assembled, Verizon offers substantially better 3G data rates for the iPad than AT&T does -- at least for those users who want to be on the lowest tier. For $15, AT&T will give you 250 MB of data per month, whereas for a mere $20, or just another five bucks, Verizon will give you 1 GB of data -- that's four times the amount from AT&T. If you want to keep it on the lowest tier, Verizon is the way to go.
The next AT&T tier is 2 GB for $25 plus another $25 for another 2 GB if you go over your original allowance. If you sign up for AT&T's postpaid plan (meaning your credit card isn't billed, but your iPad data plan shows up on your AT&T monthly statement instead), AT&T offers those customers an extra 1 GB of data in $10 increments. If you opt for the postpaid method, 3 GB of monthly data will cost $35, 4 GB of month data will cost $45, etc. If you opt for the prepaid method, 4 GB of data will cost you $50.
For the $20 1 GB entry-level Verizon tier, you'll pay $20 for every gigabyte you go over, so 2 GBs will cost you a whopping $40. In that case, it's better to hop on Verizon's next tier of 3 GB for $35, which matches the total $35 price of AT&T's 2 GB + 1 GB overage charge. Verizon also offers 5 GB and 10 GB tiers for $50 and $80 respectively.
You'll have to cut the math for yourself when you decide which 3G iPad 2 model to go with. It's tricky to get a full hold on what exactly a GB of data will cost you on AT&T, since you need to decide for yourself if you are going the prepaid or postpaid route. However, if you are strictly getting an iPad 2 Wi-Fi+3G and you're only expecting to use the 3G services from time to time, you get four times the data allowance for only a 33 percent rate increase if you opt for a Verizon iPad over the AT&T one.