Google, at least until the advent of Buzz and Google Plus, seemed to keep the user experience first and foremost (they're rapidly losing this vision).

Yahoo turned to face the siren song of advertising and eyeball aggregation, damn the user, by the end of the 1990s. Sure, some of their products may have shone (I was well off and away from their target userbase by that time) but as Diego said, the corporate DNA of organizing the Web, was lost.