I didn’t make this as universal as possible, it’s actually for a specific shopping scenario, but if it helps your decision by some chance then all the better!

My specifics:

I’m on a shared/family plan with a total of three lines and three iPhones. All are due for an upgrade (although we might just upgrade two of them).
Average data consumption is a bit over 3GB, so any plan needs at least 4GB of data. Average call time per month is about 1,200 minutes total, but nowadays all carriers have unlimited calling and texting as we shift to a data-only model. Lastly, each person would be upgrading to the iPhone 6 with 16GB storage.

Findings:

comparison of carrier cost for new iPhone

Lastly, I didn’t include the trade-in discounts with the grand totals, but you can find the respective trade-in offers in the “fine print” at the bottom of the chart.

Visual Mockups

Comparing phone plans for the latest iPhone upgrade

Gallery