The interjection expressing approval, exultation, or encouragement is variously spelled hurrah, hooray, and hurray. There are also some older forms—hurra, hurrea, and whurra, among others—that are no longer in use. All come from the older huzza,1 which itself lives on though is less common than hurrah and the rest.
Hurrah is more common than the others and has been so a long time. This is probably explained by the fact that hurrah doubles as a noun (referring to an instance of the interjection, usually in the phrase last hurrah, which refers to a final effort or appearance) more often than the others. But searches of current news sources from around the English-speaking world show that, in all main varieties of English, the interjection is spelled hooray at least as often as hurrah, while hurray is a distant third.
The ngram below graphs the use of hooray, hurrah, and hurray in a large number of English-language books published from 1850 to 2000. Of course, it doesn’t show how they’re used, and some of hurrah‘s ascendancy is no doubt explained by its doubling as a noun, but it does suggest that hurrah is the preferred form, albeit perhaps less so now than in the 19th century.
Hooray! Tom Cruise is back! [Irish Times]
Now, he said, it is going so well that what started off as a romantic last hurrah is going to continue into 2013 and beyond. [The Australian]
Hooray for the socialist from Bain Capital! [New York Times]
Hurrah for Sir Paul Coleridge, who, like his poetic namesake Samuel Taylor, is a big old soppy romantic at heart. [Telegraph]
So hurray for those who caught the freeze frame of an online betting site on his laptop! [Wall Street Journal]