it's been a long time since I was on a road trip, but the best deal I found was Verizon. The only blacked out areas were between Pecos and El Passo in TX, and northern Alabama.
Now I have Verizon wireless for my computer.
It is fantastic, 4g
but I live in a college town
when I get up to Indiananpolis at my parents house out in the suburbs, it is 3g and very slow
when I was constantly roadtripping, most had ATT and some thing else as a back up if it was critical.
But if it was me, I would start out with Verizon, and add another service if it ever became a problem.
verizon wireless is only $50/mo, 5gb, and that's more than you will ever need for trading, an extra $10 bucks a month if you start watching a lot of u tube