The difference is understandable - all of the sites measure different data. W3Schools simply measures its own traffic, and, as a web development education site, it is likely to be visited by people with more of an interest in non-IE browsers. (The site has an Alexa ranking of 220, however, giving it a large sample size.) StatCounter tracks visitors to a network of 3 million associated sites, while NetMarketShare counts unique visitors to a smaller network of 40,000 sites. It's easy to see why the numbers can look so different.
But it certainly makes it tricky to say unequivocally that one browser is the one to beat, and that's part of the reason why the browser question is the subject of such a big argument in the tech world (and this doesn't even include mobile browsers, a relatively small market for now).
Either the most-used or second-most-used browser in the world, depending on whom you ask, Chrome has rocketed to prominence since its introduction in 2008. A browser made by the Internet's most powerful company could hardly fail to gain some traction, but the speed with which it has achieved seeming parity with Internet Explorer surprised many - not least those behind Mozilla Firefox, which had labored mightily to reach a respectable second place behind IE.
Chrome's focus on performance and simplicity has paid off well - through its many versions, which are deployed quickly and silently through an automatic update process, the emphasis has been on a smooth, streamlined experience.
Criticism of the browser generally centers on privacy issues. Soon after it was launched, there was an outcry over the Suggest feature, which transmitted keystrokes back to Google HQ. Google's business model, which depends on the use of personal data for accurate ad targeting, hasn't won it many favors among privacy advocates.
The long-time unchallenged leader of the pack, IE is no longer quite as dominant as it was a decade ago, when few used any other browser. However, time and anti-trust litigation notwithstanding, Microsoft's browser still commands a huge user base.
Competition, in a very real way, has been a positive thing for IE, forcing Microsoft to modernize and innovate far more rapidly than it did during its unchallenged period. The past few versions - most notably IE 8, 9 and now 10 - have all boasted substantial performance increases and added support for new standards like HTML5, designed to bring it more into line with Chrome and Firefox.
Still, particularly among highly technical types, a powerful dislike of IE runs deep. Saying "IE 6" to a web developer is practically guaranteed to provoke gritted teeth and shudders of frustration (at least!), thanks to a widespread perception that Microsoft's lack of innovation held back the development of new web standards for years.
Microsoft has worked to overcome that antipathy with recent versions of the browser, but is it enough to recover an unchallenged lead in the market?
Since 2004, Firefox has been stuck as a perpetual second-fiddle - first to IE, then to Chrome. It's perhaps a little unfortunate that the browser that first began to erode Microsoft's iron grip over the marketplace has never enjoyed its own period of dominance, but Firefox nonetheless has a huge number of users, and is said to be the most common browser in many parts of the world, particularly Europe and Africa.
Firefox was the first to introduce tabbed browsing, also known as "the reason why you don't have about 46 different windows open on your desktop right now," and pioneered an ecosystem of plug-ins, allowing users to modify the browser in many ways. An open-source project - curated and managed by the Mozilla Foundation - Firefox is dedicated to open web standards and helped bring about a climate in which they could thrive.
Unfortunately, however, the past year or so hasn't been particularly kind to Firefox. It's now pretty clearly in third place behind Chrome and IE in terms of market share, and missteps like a me-too move to a rapid development schedule irritated crucial enterprise users.
While it still has a vital development community and millions of users around the world, Firefox has to make a big move to catch up with its main rivals - which, importantly, are both backed by enormously wealthy corporate titans.