Q:

Hurrah or Hooray? 

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? 

A:

The first two are commonly used in British English, and the latter is used in American English.  They'd all be understood completely fine, though - there's no difference in the meanings. 

A:

NOAD lists the terms this way:

hooray exclamation
  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). 