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T-Mobile is by far the best option for their unlimited plan. The rest of the inputs ignore T-Mobile because of this. Nothing comes anywhere close to them.
Sprint undercuts Verizon and AT&T on 1 line then quickly becomes the most expensive, and by a lot, on all other tiers, regardless of how much data you purchase on AT&T and Verizon.
With 4GB of data, Sprint, AT&T and Verizon are virtually identical, but stepping up to 10GB on 1 line gives Sprint the lead in that chart. Any other choice, no matter what you do, Sprint is the worst and by a lot.
Verizon and AT&T are identical with 4GB of data. With 10GB of data, AT&T is cheaper than Verizon for every plan with 3 or more lines. With 2 lines they're equal, with 1 line Verizon is cheaper. This happens because it is $10 less per line on AT&T, while Verizon starts their tier off $10 cheaper.
By # of lines:
If you are going to get 1 line of service and only 4GB of data, it doesn't matter who you choose. Sprint is cheaper if you are a big data consumer.
If you're going to get 2 lines, no matter what AT&T and Verizon are equal and both cheaper than Sprint.
If you're going to get 3 lines of service AT&T is cheapest, then Verizon then Sprint.
If you're going to get 4 lines of service AT&T is cheapest, then Verizon then Sprint.
If you're going to get 5 lines of service AT&T is cheapest, then Verizon then Sprint.
To directly answer the question of the initial post: With 5 lines of service, Sprint is $207 more expensive than the next most expensive, Verizon. That margin slims by $59 for every line less than 5, until at a single line, Sprint is the better value.