You can just simplify this to mean "It's good (the taste)" in which case おいしい! is what I hear most often. I don't think there is a specific rule to follow when it comes to this kind of structure since there are so many ways to express this in Japanese depending on what it is you're talking about. You might want to study up ~そう (the food) looks good = おいしそう (that tv drama) sounds interesting = おもしろそう

They're both right but I guess it depends on where you want to place the focus. 今日、椅子を買わない. I won't buy a chair today (and you're not going to buy anything else, either) but 今日、椅子は買わない (as for a/the chair) I won't buy it (but I'm still going to buy other things).