Currently the answer is none.
IE is crap for all of its compatibility problems. Maybe they'll improve in the future.
Firefox is not responsive, buggy and you get tempted by extensions which make it even more unstable.
Chrome is kind of good, but it's by google who spies on you and misses some features I'd like
Opera was until recently the best browser, but for the last few years it has really started to go downhill with lots of pointless features arriving aimed for 'n00bs'. It has also started to get more unstable and there are many bugs that haven't been fixed (altough it's not as worse as IE/Firefox).
Overall, I would still choose Opera. It's fast, has probably all the features you need without extensions, also has support for stuff you maybe don't use often enough to have a dedicated application for (torrent, email, irc, rss etc.). It also has support for syncing your settings and bookmarks with other computers.
I'd say that the best 'just browser' currently is Chrome but as said before, you're telling the google empire even more than they already know about you (which is a lot).