It's not a case of "who is the best" but rather "who is currently the least worst"

Three is named (joint) worst network in the UK by the official telecoms regulator (part of the UK government).

Called them multiple times, no-one would tell me why. Went to a Three shop and they told me I'd been disconncted for "security" because I'd been away from the address on my account too long!

Plus their broken app and abysmal coverage in London...