Dividends and stock buybacks both distribute value to shareholders. Dividends distribute cash, and stock buybacks distribute value by increasing the price of shares. In a rational market, distributing an $X dividend or buying back $X worth of shares will both have the same result for shareholder value. See the sibling comment for details.

People who are investing with a long-term view in mind might prefer stock buybacks because it defers the taxable event until sale. I prefer stock buybacks when I'm planning to hold my shares. With a dividend, I have to pay taxes on the dividend before I can reinvest that cash by buying more shares; with stock buybacks, the share price just increases by that amount over time instead.