I used to be on vodafone years ago. Worst network to be with!
In my house I get 80mbps on EE, 65mbps on 3, never tested O2 but you get a good 4G signal but with vodafone you barely get a signal and even then its 2G!
I drove down to London last year with a friend who is on Vodafone until her contract expires and I streamed music the whole journey through TuneIn on 3 network without a hitch. She had no signal 10% of the time, 2G 50% of the time and the rest was on 3G. Only in London did she get 4G.
In this day and age where data usage has way overtaken voice calls the importance of a good fast connection is paramount. I was perfectly happy with 3 right up until they took me off my £15 one plan and have since switched to EE where I do get faster speeds and also 4G in a lot more areas.