I only use Cisco Aironet and Symbol kit - for range and resilience they do outperform every other piece of kit I have tested. Their prices are obviously a little higher (a few hundreds rather than sub-one hundred) but they are the market leaders, which is why Walmart, Sainsburys, British Airways etc use them.

From a 100mW 3dB omni-directional antenna fitted to an Aironet access point in a metal comms cage in a metal aircraft hanger at Blackpool airport, I got a range of over 1 mile using a laptop PCMCIA card with 2" antenna.

Using Symbol kit with directional 6dB Huber Suhner patch antennas I have got successful connectivity at 5.5 Mb/s at over 6 miles.

I have had longer distances with wierd antennas, but they probably don't meet licencing regs.

Of the more recent kit, Symbol appear to be the most resistant to interference (microwaves, bluetooth, etc) and for mobile Voice-over-IP, their kit is superb, managing access point handovers seamlessly, but Cisco's kit is well supported by their management utilities.