Do you need to upgrade now? Its honestly best to hold on until the end of this month as the phone situation will be a lot better.
If you need a phone now and it has to be directly from Orange, the 'best' smartphone they sell is probably the iPhone 4, followed by/tied with the HTC Desire HD, Samsung Omnia 7 and Samsung Galaxy S, depending entirely on your needs.
If you write down what you use your phone for mainly (like a list), I can assist you better.