I've been using 3's mobile broadband for years and it's just gets better, at home I'm now seeing 15MB download speeds regularly!
Only been caught out once on site but that was the north york moors! however, the recent sell off of 4g frequencies will improve things as far as that's concerned. That is, the lower band of 800 or is it 850 being able to reach much further from the mast than the current 3g 2100 band, so soon reaching where hitherto it was impossible.
Only niggle I have isboth our phones are on Three's an 'all you can eat' contracts so come with mobile hotspot to connect the laptop and anything else too, including the smart TV. The theory being my dedicated laptop dongle would be redundant, however the hotspot feature eats the phone battery!! so annoying as it is, at £8 a month for 5gig on the dongle contract, it's staying for the time being