I have been using 'Hurrah/Hurray', but when I recently saw google spam box it says 'Hooray'. Which word actually suits or which one to use?
NOAD lists the terms this way:
another term for hurrah
hurrah (also hooray, hurray |-ˈrā|) exclamation
used to express joy or approval: Hurrah! She's here at last!
Meaningwise, there's no difference between the terms. As for which one you should use, that depends on how you envision the last syllable pronounced. If you want the reader to mentally end the word with a -rah, use hurrah; if you want them to end it with -ray, use hooray (or hurray).