I can appreciate the difficulty of TS, and I think it is a cool game. I wouldn't mind owning one and the price is great. But I think you only really need one extra challenging game in your collection, because pinball is best when it's shared with others, and as has been mentioned here previously, your friends and family will play WH2O more...it's just more fun.
I have a BSD, so I don't need TS and can't speak to owning it, but I think WH2O is the clear choice for me as my friends love it in the collection, just like they do Scared Stiff. Nordman was so great at making fun, party-favorite machines in the 90s...