As jfuente11 pointed out there are still a few advantages. I just looked and before taxes Sprint for Unlimited Talk, Text and Data + insurance is $91 before tax.
Now if you want tethering that is more and with T-Mobile's unlimited plan 2.5 Gb of Highspeed tethering is included. Now with the 2.5 Gb data plan you have to remember it is actually unlimited data just 2.5 Gb of Highspeed Data you get throttled after that so if you are a day or two short you don't have to pay a for another big chunk of data for two days that you won't use all of if you can survive a day or two on 2G data.
Also remember that with Sprint an I-Phone 5s even for an upgrade you have to shell out $200 down, if you took that same $200 and put it down with T-Mobile your payment will be lower (probably close to a 1/3 lower) so again it's not like comparing Apple's to Apple's and again as jfuente11 pointed out that after you pay off the phone your bill goes down, with the other 3 carriers you keep paying for a phone that you essentially already paid for.
The other non apple's to apple's is the insurance which is $11 for Iphone 5s at Sprint (when I just ran it) and that is all it is, with T-Mobile insurance is also JUMP, so depending on when you signed up you can upgrade pretty much whenever you want + it is also insurance.
Lastly I have Sprint also (company phone so I have no choice) and there is no comparing the networks or speed. I live in ATL (acutally NW Atlanta suburbs) and can't drive from the airport to my house on Sprint without dropping at least 5 times and can make it all the way home T-Mobile and I won't even get into speed comparisons because it is not even close. So you may be paying a bit more today (again bill will go down) but your are also getting so much more.
