I was on the Simple Mobile $60 plan for a year until the Straight Talk BYOD. I've had to call customer service maybe twice in that year for Simple Mobile and it was quite pleasant. Also, with SM, You know you're going to get at least 2 GB of data before they start throttling and another 1 GB of data before they shut it off completely. Even after that, they only shut off data until the next billing cycle. If you continue excessive usage, they will terminate your account according to the TOS, although, I don't believe anyone's account has ever been terminated. I averaged around 1.5 - 2 GB a month and never had an issue.
With all that said, I still switched to Straight Talk and have been with them for 3 months now. It seems the people with the "T-Mo" Straight Talk sim are having better luck regarding data. So far all the complaints have been from people using the "AT&T" sim. I haven't changed my data habits at all despite everyone saying to use wifi as often as possible to avoid your account being terminated and you losing your number... but, I hardly ever use wifi, even at home. Once in a while, I'll stream TuneIn radio and watch a couple of Youtube videos but, so far, I haven't heard anything from Straight Talk regarding data usage. I've never had to call Straight Talk customer service but from what I hear, I hope I never have to.
If you're a data hog and you value your phone number too much, definitely stick with Simple Mobile. If you feel you can control your data usage, you're not going to find a better deal than Straight Talk.
With Carlos "Slim Shady" buying Simple Mobile, they're going to be part of the America Movil family anyway.