In a matter of just a few days, we've gone from two major US carriers offering unlimited data plans to all four. After the past few years, it seems very strange to say this, but unlimited data is back. This time around, though, these plans come with a lot of caveats, and it can be hard to keep things straight between AT&T, Verizon, T-Mobile, and Sprint. So, if you're in the market for a new carrier and these unlimited plans have piqued your interest, which one should you go with? Hopefully this guide helps clear some things up.