It won't surprise you to know that it is America.
This from the Economist
WIRELESS internet is spreading extremely fast. Today business travellers have over 286,000 hotspots around the world at their disposal, compared with 53,700 five years ago, according to JiWire, a mobile audience media company. Reflecting its early adoption of WiFi, America has most hotspots, although China is adding networks particularly rapidly. Rich countries with the most tech-friendly cultures (such as South Korea) figure prominently. Measured per person, Sweden and Britain offer the best hotspot penetration rates.