I get excellent speeds where I live (Very rural), which is surprising as virtually the whole village and surrounding farms all use '3' as a substitute for poor (< 1mbps) ADSL, despite this I rarely see below 10mbps even at peak times, even in the summer when a local caravan park is full of holidaying families.
However, in direct contrast the market town where I work, rarely see's above 1mbps from '3', and 'no connection' messages are a regular occurance and this is just inside the town centre. '3' blame this on congestion, and the fact that the two masts covering the town are not yet high speed enabled.
They have been constantly promising that the entire area is due to be fully upgraded to at least DC-HSDPA "very soon" for over 12 months now, and interestingly the town is also one that is on the list to have 4G by the end of 2014. I think that they are cutting it a bit fine, since no planning applications appear on the local Council website, and nothing about future availability of 4G is showing on their own coverage checker, it just says "Not available" and I have a gut feeling it will continue to say this well into the New Year.
I know several work colleagues who also live in the Town and who have all left '3' when their contracts expired, have since moved to 02 / Giffgaff whose Data connection speeds in the same town makes '3' look like dial up.
If I didn't live in an area which shows how good Three speeds can be, then I would probably have already joined them. Although I think the huge reduction in tethering from Unlimited to 4GB and the insult of having to stand a fairly large price increase for the privilege of getting that reduced allowance will be the final push, as the majority of my monthly usage is web surfing, I can get unlimited web access from one of the old T-Mobile 6 / 12 month data sims, for a buy it now price, which works out at about £4.50 a month.