Best bet is to pick up some free PAYG sims and use a tenner or two to test the various networks.
Lot of negative comments regards Three customer support but they must also have a lot of happy customers? I've a spare Android phone so I can trial Three more against T-Mob around my day to day area for the time being. T-Mobile don't have signal in our local coffee house - must try Three in there 
unlimited data for £25 a month is a winner!
Anyone on Three ....... what's coverage like out of major cities? In my area of 'the sticks' it seems very good.

15 quid a month PAYG 300 mins 3000 texts & unlimited data.![]()

All you can eat data is 15 quid a month on PAYG 3.
Thought you couldn't tether on the £15 a month one,3 PAYG is Superb, 15 quid a month gets 300 mins to anyone, 3000 text & unlimited data so tethering my Xoom/tablet is no prob at all.
If I was you I'd get somebody with a 3 moby to pop round to check signal strength etc or just get a 3 PAYG sim & try it yourself.
SIM plans with All-you-can-eat data do not allow tethering (except for the One Plan
All you can eat data is 15 quid a month on PAYG 3.
I am in a small town & motor about the countryside & have Never lost my signal & I've been on 3 for years now.
15 quid a month PAYG 300 mins 3000 texts & unlimited data.![]()