i'm happy with t-mobile been with them for years, still do plenty of 18 month contracts aswell, even on the desire, depends what you want, minute/text wise, but they have the best internet usage policy imo, something like 3gig on android phones, and only a polite chill out warning if you go over.
I got a desire with 900 minutes unlimited txts and internet 18 month contract (you can upgrade after 17) for £30 pm although i think thats gone upto £35 now but you get to pick a bolt on thing such as unlimited landline calls.
I've found they are best if dealt direct, i couldnt get the deal i got anywhere else, and i did try, and as mentioned, branded phones are a piece of p*ss to debrand.