Opera is by far the best - and it's free now, too by the way.
Tabs - Awesome, and done way better than they are in Firefox
Panels - Awesome
Mouse Gestures - Awesome
Completely customizable toolbars and interface - Awesome
Stable, compact, uses up little memory compared to other browsers - Awesome
The ONLY downside is that some websites, created by incredibly ignorant designers, decide that just because you aren't using Firefox or IE, your browser MUST not be able to handle the page, so they give you an error message. But this is the fault of the person who created the page, and has nothing to do with Opera itself - and you have the option to pretend you're using a different browser anyway so it's not much of an issue anyway.