Depends on what you want from your contract??....do u want more texts than call time or more call time than texts??.
A bit more info would be helpful as your asking too generic a question for someone to help u out.
Saying that though there are some good offers going round, i just recently joined up to tmobile with their flext tariffs and web n walk. Im on the £50 a month flext tariff which gives me £255 worth of call and text allowance and on top of that i get unlimited web access and email. So all in all its costing me just over £60 a month when i was spending almost £80 a month with o2, who were only giving me 1000 xnet mins and 50 texts.