THey are more or less the same these days, though Verizon still has the reputation of being more reliable. Certainly there are pockets where one works better than the other, but that's true for all carriers everywhere.

Who cares if you only have three bars in Midtown, as long as you can make/receive calls and get data service?

For a slightly cheaper alternative, I have always been a fan of T-mobile. If you stay in cities/suburbs or along interstates, the service is perfectly fine.