They are by far the cheapest big name provider. I have a $30 unlimited data/text + 100 voice minute pre-paid plan. At
None of the other providers comes close to the price, I have a Nexus 4 so I only have GSM to choose from AT&T's offering is not unlimited, it only includes 2GB of (if you don't add any more with a data package) and that's $60/mo, A comparable Simple Mobile plan(unlimited, first 4GB at 4G) it's $60 Straight Talk has an "unlimited web access" plan for $45, still more expensive than the $30 with T-Mo.
But again, my phone becomes almost completely unusable anywhere outside of the NYC Metro or inside a big building since the T-Mo frequencies don't penetrate buildings well.
Where there's a will, there's a relative.