If you want to factor in an ethical dimension too, you may find that one or two of the charities you support have an affinity card available (sometimes in both visa and mastercard flavours) – then you can be donating as you're shopping. The co-operative bank have quite a large suite of affinity cards, but it's also worth checking the websites of your preferred charity.
For years I had an American Express Red, but outside of the States it seems many hotels and retailers either don't accept Amex, or they pay a higher Merchant Fee than they do with Visa for example. Several times I've been asked if I have another means of paying as soon as they see the Amex.
As other posters have said, it sometimes pays off to have two cards on different networks (or whatever the word is), lest one lets you down in the back of beyond