What's cheaper? T-Mobile, or Sprint?

So I'm wanting do to the upgrade program with T-Mobile or Sprint. But what's cheaper? I'm wanting to get the iPhone 7 plus with 128gb. I want to get the cheapest plan tho. What would be cheaper? Cause I can't afford At&t or Verizon.

Added (1). I'm not wanting to do a family plan.

If you are going for a family plan, I would recommend Sprint with their new $90 plan; but solo, T-Mobile

What is the MOST you can afford per month? I will assume that you are wanting to get the phone on monthly installments, and that will be on top of what the plan costs, and if you are in fact wanting to pay the phone off in monthly installments, you will need AppleCare Plus or cell phone insurance to replace the phone is it get damaged or destroyed.