Sprint drove the Titanic straight into the iceberg. They drop calls EVERYWHERE now, and their data is almost entirely unusable. Them, along with their million MVNOs shouldn't be considered as an option.
If you want cheap and reliable but don't mind a coverage map that isn't the biggest, go with T-Mobile.
If you need coverage everywhere and don't mind spending the money, flip a coin between ATT and Verizon.
If you need coverage everywhere and don't use a ton of data and don't want to spend the money, get an unlocked GSM phone and get Straight Talk on the ATT network.