The cost difference from a Sprint Overdrive to the Evo 4G is 3 bucks a month here. And both have a 5 Gigabyte a month limit. Given the 3 bucks a month difference I thing the Droid wins as I can get to the net without booting my laptop.
Be aware that Spring discounts are all over the map so your deal may vary.
I plan on traveling around the US. I am considering either getting a wireless card for my computer or buying an Android phone and using it for the wi-fi connection. I currently use Sprint for my mobile service. Any thoughts on which is a better way of connecting while traveling?