They are not necessarily the first, but their 'tiers' are a nice touch.
By comparison, Consumer Cellular you can get iPhone 6 for $50 down, the rest over 2 years, interest/fee-free. For more expensive phones, they vary the down payment to keep the monthly the same. They are tops in customer satisfaction, and among the cheapest if you are under 3-4 GB/month. With my mainly wifi data usage, I'm typically at around $45/month total for 2 phones sharing a plan.
The payment plans are a nice addition (all of the major carriers provide them). Cricket uses the ATT 4GLTE network (unlocked gsm or ATT devices). It's been great for me. Customer service has been good, number was ported without problem and the speed and price unbeatable. If you're interested hit the link for a $25 credit if you sign up - https://mycricket.sparkrefer.com/55SM1XE