I first used the Orange card because of their 14 day return policy. That is: if it doesn't receive 3G in your area, and only receives the slower GPRS, you take it back and you'll be given your money will be returned and the contract cancelled.
I then realised after sometime that Vodafone offer by far the best tarriffs and on the 250 MB's download limit, they beat the rest hands down and had a verbal assurance that the same 14 day return policy would apply to match Orange .