Whats the best currency for taking to Botswana? Sterling, Euros or US Dollars?

I am answering a bit late - But please! Take note of this. All the answers above are slightly wrong. ENSURE that you have PULA, the local currency for Botswana available! At most places they only take Pula and nothing else. I know since I have been there many times, and if you get stuck without an ATM facility you are indeed in trouble.