There are many fields in which there is no clear front-runner, but with technology (and especially the Internet) that is often not the case. For example, there is one popular website that the majority uses when it comes to search engines (Google), video-sharing (Youtube), social networks (Facebook), photo-sharing (Flickr), online encyclopedias (Wikipedia) and so forth. Sometimes there are a few popular ones, but there is usually some distinction between them that makes them target slightly different audiences (e.g. Youtube vs. Hulu). Of course, a fair number of people don't use these sites that are #1 in popularity, but these people are split among many of the competitors. So I'd like to ask the hacker community here: do any of you choose to use an alternative to one of these top websites and, if so, what is your reasoning behind it?

And as a parallel question: Do you think that the top websites are at the top because of their polish, usefulness, recreational value, luck, or something else?