How should I begin the process of selecting a standard -- 802.11a, 802.11b or whatever is coming next?
Most of those purchasing new WLAN equipment today should probably buy 802.11g or dual-mode 802.11a/g products.
Home users with one or two laptops and a broadband connection may not need or even notice the extra bandwidth provided by 802.11a or 802.11g. However, most entry-level 802.11g wireless routers cost little more now than 802.11b routers. 802.11b routers have probably been sitting on shelves a while, so why not purchase newer products? Many new 802.11g routers already support WPA, so you'll get better security, and vendors are more likely to issue firmware upgrades and fixes for newer products. Why 802.11g? Because 802.11g routers will interoperate with the 802.11b adapters that ship with most laptops today, but 802.11a will not.
Business users may benefit from the additional capacity provided by 802.11a or 802.11g access points. 802.11a can be a better choice for backhaul links (e.g., bridging between two building networks or connecting a wireless server) because the aggregate capacity of several 802.11a APs is higher and less subject to interference from stations using 802.11b/g or Bluetooth. 802.11g can be better for situations where interoperability reigns supreme (e.g., private or public hotspots that can't control the kinds of cards used by stations). In fact, depending on business needs, springing for dual-mode 802.11a/g APs can maximize interoperability.
What about cards used in wireless stations? There, recommendations are less clear-cut. It can be more convenient and less IT labor-intensive to purchase laptops with 802.11b on board than to add third-party 802.11g PC cards. Even a small price difference in cards adds up when you're purchasing in volume. On the other hand, if you ARE purchasing PC cards, then dual-mode 802.11a/g cards offer more flexibility. Yes, these cards may cost more, but good buys can be found if you look around.
The next WLAN standard will be 802.11n. Although you may see pre-standard 802.11n APs with MIMO hit the market later this year, the 802.11n standard has barely gotten started, and it won't be finished for quite some time. Businesses with large latency-sensitive WLANs -- for example, those using VoIP over 802.11 -- will be the early adopters that go for pre-standard 802.11n products. The rest of us will probably stick with 802.11a/g for the next year or so.