1. In a small bowl, whisk together vinegar and oil. Rinse and core tomatoes and slice 1/3 to 1/2 inch thick. Arrange in layers in an airtight container or on a serving dish, drizzling vinegar mixture and sprinkling mint, basil, salt, and pepper evenly over each layer.
2. Cover and chill at least 30 minutes or up to 4 hours. Bring to room temperature before serving.
If you're packing a picnic, assemble this salad right in the container you'll transport it in; otherwise, layer it on a serving platter.