All the networks have their problems with customer service. And all the networks use 1800Mhz for coverage in cities, too. The major difference between them is the billing packages and the choice of handsets, not technology or service.

Vodafone and O2, unlike T-Mobile and Orange, allow 3rd party "service providers" to arrange billing too, and the service offered can vary incredibly.

There are also virtual operators to consider, the biggest being Virgin Mobile, who often have good deals (but less cutting edge handsets sometimes).