It's a little unfair to call T-Mobile the worst network in the nation without explaining what you mean. T-Mobile does not have the most widespread coverage, that is true, but coverage is not the only thing that matters. They do have the best deal on service by far. Unlimited minutes, unlimited text, unlimited data, and unlimited tethering for $79.99 and no contract. You couldn't get that level of service from Verizon even if you paid $150 a month.
You get service in less places than Verizon with T-Mobile, but you get a ton of value for what you pay and if you live and work in an area with good coverage, they are a fantastic choice.