No browser is 100% safe
This is the key. All of them have their ups and downs, there is no "perfect" browser.
IE is the most targeted by virus developers, simply because it has the largest market share. The same goes with Windows vs. Linux: Most viruses are on Win because 90% of computers has Win installed. Simple as that.
That being said, Internet Explorer 9 is considerably better than the previous versions: faster, more stable, more user friendly, and so on. But since it is compatible only with Win Vista and Seven, those people still using XP are cut out.
Firefox: great, lovely browser, highly customizable. It has some flaws when it comes to websites which were developed with IE in mind (developers' fault!). But the thing that I hate about Firefox is Mozilla's choice to release a MAJOR version every three months! This means that many plug-ins suitable for version 7 won't work with version 8, for example. That's simply too much, too fast and unconceivable in a corporate environment. And that's why I don't recommend Firefox anymore, despite its undeniable quality.
Google Chrome: fast, light, essential. But with the same problem as Firefox: major releases rushed out every few months. Overall a solid browser, only a bit too invasive (toolbar, updater, etc.)
Safari: simply put, it's perfect for Apple Macs but suffers on Windows. It's got all the bells and whistles you could ask for, but you can tell it was conceived for Macs and that's the environment in which it has no rivals.
Opera: last but not least, to me Opera is the best alternative to IE on a Win platform. It's up to date, it's reasonably fast, it's solid. A few minor flaws but I repeat, to me it's the best choice to replace IE.
Only my 2cents, of course