of the two choices you are giving i would have to say the Mozilla Firefox, I feel it is more advanced than Opera, but given a choice hands down, i prefer the Advanced Browser. it has many more options than either Mozilla Firefox, or Opera, and being a tabbed browser you can choose to have more than one home page, it has a built in pop up blocker, and you can easily clean your cache, cookies, and temporary Internet files right from your browser, plus has the features of Internet explorer built into it. Surf the Web Faster! This browser was built for speed. You will get less crashes and lockups with this browser. World class engineering and design - this browser is the best on the planet! Rock solid performance - includes memory enhancer that outperforms all other browsers in it's class. Best of all it is 100% Free - No Adware, No Popups, No Spyware - just one great browser for you to enjoy!
Here are some of the advanced features of Advanced Browser:
Super fast browsing architecture!
Built-in Popup Killer
Ability to turn on/off Flash Animation
Quick Search Toolbar
Site Group: Open and save a collection of sites as a group
Built in Erase tool to remove all traces of online activity
Adds level of security to your browsing experience
You can change the Skins to your color preference
Rock solid performance over all other browsers, and it's free. Check it out sometime and see what i mean...