In my everyday English, I frequently use the "What I like about something" structure. However, I'm not certain whether it can be complemented with both forms: "is that" and "is".
Let me illustrate my question with the following example:
What I love about New York is that it's so big and vibrant.
What I love about New York is it's so big and vibrant.
What I love about the US is that you can feel comfortable saying what you want.
What I love about the US is you can feel comfortable saying what you want.
For some reason the sentences with the word "that" sound better to my ear than the ones without it. Is it just me, or does the version withouth "that" sound a bit off? What is your opinion on the matter? Are both forms gramatically correct? Is it just a matter of style?