You cannot go wrong with either! Both have excellent food.
Consider, though, that Y&Y is a sitdown, so food is theoretically cooked to order, while TH is a buffet, so food is cooked in larger quantities. (Food is usually still very fresh, as turnover is high.) There is also a limited number of choices at Y&Y compared to TH because of their different styles, and accomodating your food for preference is more difficult and may not be able to be done at TH. TH does give you the opportunity to try many new things and get more of the things you like.