The ESP8266 seems really interesting, however, until I can order 500-1000 from a reputable vendor in trays / tape and reel I'm too scared to think about using it for a small run product.
I prototyped a CC3200 module but stopped working on it when it became apparent that the ESP8266 was here to stay. It's a simpler chip with fewer available GPIO pins and less processing power, but it can be packed into a much smaller area than the CC3200 (CC3200s require 3 separate power inductors!).
It's important to note that the ESP8266 may well be more open than the CC3200! Much of the CC3200's functionality is packed into a binary blob from TI, and the chip runs this code on a second core that you don't have any control over.
I only know what I've read. That said, take a look at the FCC certification document for the ESP-12: https://fccid.net/number.php?fcc=2ADUIESP-12&id=253176
Notice that it is certified as a "single modular" device.
The FCC requires that single modular devices be totally self contained: http://www.lsr.com/white-papers/fcc-guidance-on-transmitter-... https://www.fcc.gov/oet/ea/presentations/files/oct09/Modular... [PDF]
The ESP-12 module does not have onboard voltage regulation. Thus, it is not totally self contained and its certification is meaningless.
Regardless of the above discussion, these modules do not have a marked FCC ID, so any certification they do or do not have is meaningless.
Like I said, I only know what I've read. I don't understand how they reached certification without onboard voltage regulation, but they did. I don't know if that means the certification will be voided, but I certainly wouldn't want to be selling a product using these modules right now.
https://www.particle.io/prototype
$10/12 Broadcom chip + STM32 chip. It's not market yet and I don't like the idea of being tied to a 3rd party platform / API. There doesn't seem to be anything in the >500 units, <5K units space that really makes sense. Near the high end of that I assume you can probably roll the intentional emitter cost into the unit cost though.