If you are still using internet explorer I would recommend getting firefox. Firefox is much more secure making it harder for people to hack into your sessions to get valuable information when you are trading online. It's a small step but a good one. Firefox also has many other features that aren't offered in IE. You can download firefox from www.mozilla.org Happy Trading!
Opera is ok, I have tried it, but if you don't pay you browser ads, kinda annoying. Firefox works fine for me.
As of last September, Opera has removed all ads from their browser. However, I would still recommend Firefox over Opera for the extensions. Opera's UI might be a little nicer, but Firefox's huge library of user-made extensions lets you do practically anything with your browser. Microsoft finally got around to including a popup blocker with IE, but Firefox's ad blocker extensions are still unrivaled. I surf for hours each day, and I honestly cannot remember the last time I've seen a banner, poster or text-based ad... and there are tons of other neat little extensions that do everything from enhance the appearance (Colorful Tabs), to increase the download and rendering speed (FasterFox), to provide extra functionality (ForecastFox, Gmail Notifier), to increase security without sacrificing usability (NoScript.) I'm sure Opera has extensions too, but Firefox's fan base is simply much larger. I doubt Opera has an auto-updating blacklist-only adblocking extension. Finally, Firefox is a completely free, open source project. Even if you don't believe in supporting FOSS for philosophical reasons, the fact that Firefox is released under the GPL means it can NEVER legally be taken away from the community. No one can ever charge money for it, or keep the source code a secret.