It Starts With the Chips
Only a few manufacturers supply the chips that reside in wireless NICs. Every wireless NIC must have a high-speed radio modem to manage transmission and reception, as well as a baseband processor responsible for digital functions, including all the framing and access that take place at the MAC (Media Access Control) layer.
Although it was once common for ODMs to combine different chips from multiple suppliers, the trend today is toward integrated chipsets. Atheros Communications, Broadcom, Intersil and other wireless semiconductor vendors promote packages, increasing competition among wireless chip developers. This translates into enhanced functionality at lower prices. Chipmakers develop reference designs that include both hardware and software marketed to multiple ODMs.
WLAN NIC Checklist
1) Driver availability for required OSs
2) Compatibility with WLAN standards: 802.11a, 802.11b, 802.11g
3) Suitable performance and range
4) Value-added features for survey and monitoring, security and diagnostics
From an enterprise perspective, the role of the chip vendor and ODM is arguably more important than the role of the supplier, because fundamental functionality usually resides in the hardware. Although it is possible to add functionality via software, the results often mean a substantial performance hit. For example, in the early days of 802.11, some cards that performed WEP (Wired Equivalent Privacy) encryption using software took a performance hit. And some differentiators--antenna quality and radio receiver sensitivity--are almost exclusively hardware.
Some chip suppliers may claim better range or better power efficiency, but as the market matures and engineering knowledge diffuses, product differentiation becomes more challenging. It's not uncommon for vendors to resort to proprietary features. An example is the turbo-mode offered on some 802.11a products, which binds two 802.11a channels together to double the raw data rate.