3 months in London coming up. All the comparisons I see online appear to be from a year ago. Here's a couple questions for the savvy Londoners:

How prevalent is WiFi in the city? This could save on data charges if WiFi is readily available.

Best signal/connectivity? In my area of northern NJ it's Verizon hands down. AT&T is a distant second, and neither T-Mobile nor Sprint deserve even to be mentioned. They're networks are just too poor in my area.

From my sparse research it appears Three is the network to choose. A couple Pounds Sterling one way or the other is meaningless as we're talking about 3 months. Is there any reason to steer clear of Three? Am I missing something that an insider can tip me off about?