Lte in other cities is not important to me. I dont travel frequently and when i do i occassionally, 3g will suffice. Since both devices will work overseas it all comes down to coverage in the NYC area and price for data usage.
if you plan on keeping your iPad for only a year, makes sense to enjoy the faster att speeds you will have while it has less users than the verizon network.
after a year, with the new iPhone and other lte phones, both networks should have similar speeds. verizon does have plans however to complete their buildout by the end of next year (they are converting all their 3g into lte). att at this time is only starting to get rid of their edge network.