AT&T or Verizon? Data wise speaking?

I mostly use my iphone for texting and data. I currently have sprint, and looking to leave them. Because my data is slow or won't have connection in certain areas. I'm looking for a carrier with faster data with more coverage areas.

AT&T-The fastest, but not by much
Verizon - The second fastest, but it is rare you will ever be without a connection.

Verizon. But Verizon is also the most expensive. 1GB of data is $50, 2GB is $60, 4GB is $70, 6GB is $80, 8GB is $90, 10GB is $100.