Atheros chipsets tend to not require any non-free code (be it on the driver or firmware side), including their USB wifi dongles. I've had mediocre (at best) experiences with them, however, what with frequent stability and signal strength issues on what I'm pretty sure to be the hardware side (though I've found this is true of pretty much every wifi chipset out there, so I guess it's okay relatively-speaking).
This used to be true, but since Qualcomm bought them out, they have done a complete 180 and basically reverted to totally closed designs (closed firmware, closed drivers, no spec sheet). The 9xxx chip-sets (which are only 802.11n) are the last ones designed before Qualcomm took over, the 10xxx chip-sets (802.11AC+) are closed and completely locked down, you cant even change your MAC address its all stuffed into a giant psuedo-driver firmware blob.
Things are getting worse, not better, on many fronts when it comes to user freedom and control over their devices. Apparently many responsible engineers in this area lack the ethical consideration of their work. The more I see this, the more I worry about bridges, airplanes, and every other piece of technology that is developed by engineers that may or may not have ethical principles.
