The teak we use in our teak furniture is absolutely "the best" hardwood used to manufacture garden teak furniture. Our teak furniture is "the best" because it is heavy, dense, and has a high content of natural mineral deposits that effectively repel water and moisture, making it "thermally stable" (no warping due to changes in climate / temperature), and highly resistant to decay.
If you leave your teak furniture untreated, the teak weathers gray naturally over time, through exposure to the sun, wind, and rain.