I do also use Opera a lot, but my main browser is still Firefox. Personally I cannot actually tell that much difference between them any longer as both seem to render pages and work just as well for most tasks.

Each has it's own unique ways of doing things so it is just down to which you prefer. For example I prefer the auto complete login method of FF over Operas Xtrl+Enter method, and I love the new Spellchecker built into FF. However, I do prefer the page scaling feature in Opera over all other browsers method of just enlarging the text on a page and buggering up the layout.

As for IE7, I hate it with a passion that surpasses even LowercaseE's hatred of Sony!