If so which would be best for rural coverage.
O2 are the only network with a legal obligation (in their licence from ofcom) to hit a percentage target.
They all have bought 800mhz frequency space which should give the longest reliable distance from a mast, similar range to the O2 and Vodafone 2G services today.
So in theory if you can get O2 or Voda 2G service, you could very likely get 4G in the next 3 years, even when you haven't had 3G from that provider.
EE is building using 1800mhz so far, so if you could get Orange or T-Mobile 2G then you could get 4G, even without any 3G.
The higher the frequency the less distance it travels in open space - BUT - the less number of concurrent users it can support. All UK networks (and all EU) use 2100mhz for 3G.
Hope that helps.
James BT Infinity 2 19/09/2012 - Sold 42/6 - Getting 46/8 - Sync 50 / 9 Mbps @ 470m approx
14 years of broadband (ntl: cable to BT FTTC) - Router: Asus RT-N66U - Modem: Huawei HG612 speedtest