I use (and voted for) Firefox.
I personally prefer Firefox and that is why I use it. It does have excellent adblocking features but only if you download the plugin. I like the download manager but it doesn't always remember to ask me about my downloads which IE always did. Also, Firefox seems to give me more unnecessary messages than IE did.
My verdict - If you are really comfortable with IE and would be uncomfortable changing, stick with IE it's not as bad as people make out. However, if you are confident with changing browser, try Firefox, it's a tiny download, it's free and you'll probably like it more than IE.
Firefox vs Opera.
Firefox is free. Opera is only free if you have ads taking up most of your browsing space. No contest. Firefox wins every time!