Hi. Ohio State U. has a good fact sheet on growing tomatoes that you can access here. It says “For optimum flavor, tomato fruits should be allowed to ripen fully on the vine, but should be picked before they begin to soften. Tomatoes that have reached mature green stage can be harvested and allowed to ripen at 60 to 65° F indoors. In autumn, green tomatoes can be harvested before early frosts damage fruits.” Although it doesn’t talk about sweetness explicitly, I think that would be included as part of “optimum flavor,” especially since many varieties of tomatoes are not intended to be sweet. So, in general, you should leave them on the vine until fully ripe. However, it may be better to harvest them earlier to avoid storm damage or sunscald (if that could be an issue), as noted in this article from Penn State U. Additionally, periods of hot weather can accelerate the softening process and slow color development. Therefore, this article from the U. of Illinois suggests that you harvest them every two days and let them ripen fully inside during periods of hot weather.