Are most people going on the G platform vs. the A? Some people say that A is better because the 5 Ghz range has no other interference?
Recent numbers indicate that 802.11g products are selling better than 802.11a, but that trend may not hold long-term. A big advantage of 802.11g over 802.11a is that G is compatible with 802.11b, which means that any laptop or PDA with an 802.11b adapter can (usually) work with an 802.11g AP. The same can't be said for A.
However, dual-band 802.11a/b/g adapters are selling well, creating an environment where client devices can communicate with either 802.11a or 802.11g APs. If dual-band adapters become the norm, then 802.11a APs will become more broadly interoperable. Dual-band 802.11a/b/g APs are also on the rise, particularly in enterprise-class APs where client diversity is common and must be dealt with now.
802.11a has two main advantages over 802.11g: channels and interference. As you note, A uses a different frequency band that's less congested and therefore less vulnerable to interference from Bluetooth, cordless phones, microwaves and other devices that operate in the 2.4 GHz band. The 5 GHz band used by A is also wider, supporting up to 12 channels in the U.S. as compared to 3 for B/G. More channels not only reduces interference, but also allows higher-density WLANs (i.e., more capacity in one spot). For this reason, 802.11a is popular for backhaul wireless links that carry aggregate traffic from one network to another.