Rate of Convergence for Infinite Series

Which of the following correctly ranks the infinite series below from the fastest rate of convergence to the slowest? A divergent series should be ranked as the slowest.

(i) $\sum_{n=1}^{\infty} \frac{1}{3^n}$
(ii) $\sum_{n=1}^{\infty} \frac{1}{2^n}$
(iii) $\sum_{n=1}^{\infty} \frac{1}{n^2}$
(iv) $\sum_{n=1}^{\infty} \frac{1}{n}$