Not my experience with 3
I still have a 3 dongle and for most of the Midlands (Leicester, Nottingham, Derby, Brum) its bloody appalling. Average speeds rarely exceed 250kbps downstream and upstream is under 100kbps. At peak times you can forget it - websites like news.bbc.co.uk simply don't work as the connection is so slow that most of the links on the page have timed out.
Nothing to do with signal strength either. Overloaded backhaul is the problem - not surprisingly since 3 own little to no infrastructure outside the M25.
One thing to watch is that speedtest.net (and others) is frequently given higher priority than other sites simply because of articles like this.
I wouldn't wish 3 "broadband" on my worst enemy.