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Buybacks are economically equivalent to dividends for a company, however they don't come with an expectation of future buybacks like dividends can (where if you drop your dividend, a lot of investors head for the door; you can stop doing buybacks and nobody notices).

For a taxable investor, a dividend incurs an immediate tax, but a buyback doesn't; if you were going to reinvest the dividend, a buyback is better. If you wouldn't reinvest the dividend, you could sell x% of your shares and some of the proceeds would be return of capital, so assuming long term capital gains, that's also better than a dividend. In tax-advantaged, there's no real difference.

Spending on R&D vs dividend or buyback is a different issue. Tech companies tend to have pretty high profit margins, so maybe they ran out of things they'd like to spend money on... it's not the worst thing to return it to investors rather than horde it or spend it on foolish things.