I, too, like Opera so much I’m willing to pay to lose the ads. To be fair, the ads are not really noticeable. They’re not very obtrusive.
Mozilla is good, too. They’re both pretty equal, but what won me over to Opera was the mouse gestures. Right-click and flick the mouse to the left to go back a page, flick to the right to go forware, up and down to reload and make an “L” shape to close the page. Love, love, love my mouse gestures.
Both have a built-in pop-up blocker. You can accept pop-ups, refuse all pop-ups or only accept requested pop-ups generated by some overt action like clicking on a link.
Both have tabbed browsing, are highly configurable, are faster than IE, etc… Really, for me, it comes down to those wonderful mouse gestures.
Congratulations for trying something new. IE is stagnant. A different browser can really make the whole internet experience more enjoyable. One word of caution, though, is some e-commerce sites use software tailored to Internet Explorer and do not display correctly in other browsers. Not all, but many.