There is a huge battle to gain new customers so usually you can be choosey and look for what suits you better and negotiate for discounts or extras. In the shops you can get to talk with the sales staff and tell them to give you their best. Compare and decide.

There are sites that represent all mobile networks and usually they are the best agents to get better deals. Companies like the Carphonewharehouse or Dial-a-phone are the most famous ones. You need to make sure they have branches on the street in case you have trouble, so that you can go and make claims.. dealing online can be hard work and companies tend to be evasive.