Which provider in the U.K. should I choose for an unlimited data plan?

Virgin Media. They have a better coverage of 3G and 4G signals as they use EE's signals and EE covers around 98% of the UK (3G signals) and have a better 4G coverage area (more) than Three. And they offer unlimited texts, unlimited calls & unlimited data (mobile internet) for around £15 a month. £2 extra for better coverage is worth it I guess? But everything depends on the city you live in.

3, they do unlimited data plan for about £13 a month i think. Also you get fast internet pretty much anywhere with a signal. 3g in most places and 4g in a lot of cities.