In reply to riff156:
Rule of thumb* is that
EE = Best for 4G coverage and performance (i.e. capacity)
O2 = Typically best for voice coverage, worst for data
* in reality coverage and capacity vary massively, get a PAYG SIM if your thinking of signing up for a contract and try before you buy/commit
Other point is if you have no mobile coverage at home consider a network which offers native Voice over WiFi services (EE, Vodafone) on the basis you are getting an iphone/phone from the MNO. O2 and H3G offer this but you need a application which is clunky.
Post edited at 14:14