I think I'd only use Yahoo! ironically these days, FF. Oh look! while I was in the newsagent's buying some fags, I got a parking ticket. Yahoo!
EDIT: No, forget that. I would use Yay! there. I don't believe I ever say Yahoo!
The one I generally use when I win £23,000,000 on the lottery is pronounced Weh-hey! ~ I don't know that I've ever seen it written down ... until now.
"Woohoo" exists more commonly as a sound (rather than written) Nun-Translator - have you ever heard the song "Song 2" by the English group "Blur"? - there´s a very famous "wooooohoooo!" in that song, it´s worth a listen to hear a fine example of the genre.
I imagine Manchester provides a lot of "woohooing" and quite a few "get in"s as well. I once saw UEFA match in the centre and definitely heard all manner of woohoos and assorted interjections there, a lot of them I couldn´t imagine how to write... Oh, and I reckon a few "wahhhey"s as well - I heard that a lot in Bristol with the lads.