Network managers assume they must choose between 11a and 11g when building a WLAN. That's just not the case. Yes, the cost of a dual-band, dual-radio enterprise-class AP can be 20 percent greater than an 11g-only model. But with the cost of APs falling, that's not much of an added expense, especially when you consider that installation costs sometimes exceed equipment costs.
Another common mistake lies in looking at the installed base of laptop users and concluding that because only a fraction have dual-band radios, it won't pay to add support for 11a. Not true. With a price premium of $10, almost every organization should provision dual-band radios on their clients. Notebook manufacturers also are increasingly installing 11ag NICs on enterprise systems by default, so the extra cost is invisible.
Finally, once 11a client penetration increases, your life will be a lot easier. Even if only 20 percent of your users connect over 11a, that translates into improved performance for every single user because it reduces contention in both bands. Plus, channel planning at 5 GHz is much simpler because there are many more nonoverlapping channels, which virtually eliminate co-channel interference.
For enterprise Wi-Fi, the choice is both 11a and 11g, not one or the other.