Safari 7 on OS X Mavericks is great and really fast. I love the iCloud keychain integration and the autofill function for passwords and credit cards. Add to these features the great OS integration and you have a winner.
Before Mavericks I was flirting with Chrome, but now I don't even consider it.
Use Safari just in case, for banking sites and the like, but have Better Touch Tool ot make web browsing excellent with both Safari and Opera - ie i use gestures on the trackpad to open a new tab, close a tab, open a link in a new tab, go forward or back, and go to the tab to the left or right of where i am... all gestures.
One extra gesture on Opera to open the side bar where i use the Opera email client to read and download all my email etc.
So, i'm 'on the net' why arse about with another 'app' for email when my browser deals with it just fine? Sadly, Opera's latest brainstorm ( brain'fart' ) is to remov the email client.... sigh.
Firefox. I just recently tried Safari again because 1Password (vers 3) broke under the latest Firefox, but after a month of trial I bit the proverbial bullet and bought 1Password 4 in order to go back to Firefox. I can't nail down exactly what I dislike about Safari, but I just don't like it.
Today, I'm using Chrome but I switch back and forth depending on what I'm doing or sometimes just how I feel. I use Chrome, Safari, and Firefox pretty interchangeably, but each has their pros and cons.
I use an older iMac running 10.7, a Macbook Air with 10.9, an iPhone 4, an iPad 2, a Samsung Chromebook, and a Win7 desktop at work, and I haven't found anything that I like to use everywhere. I also use minimal extensions and plugins, mostly just Flash. I use TabToFront in Chrome and MacDict in FF, and the default themes. I tried Glims for Safari for a while but it really jacks with performance and stability, and the latest version throws ads at you.
Firefox has the best UI and is the most configurable but it has a memory problem over time. The longer it runs the more RAM it eats and wont release, even when using the reset in about:memory. Once FF gets over 500Mb of RAM, you'll never get it back without quitting. It's also the lowest scoring on most benchmarks and visibly the slowest on my iMac. I've also found some niggles with the way Gecko renders some sites, but they are few and far between and I believe they are coded more for IE than HTML5 compliance.
Chrome is the highest scoring on most benchmarks, best HTML5 and CSS3 compliant, and it's fast... but the cost of that speed is a little more RAM and running my CPU temp up. I've had it suck my MBA battery dry in less than 4 hours... Safari and Firefox will run for over 6 hours hard use. Chrome for iOS seems to use a bit more battery but I've never really timed it. It's also only 32bit so Java 7 is not supported. Some Flash content and almost anything using WebGL will run the fans at high speed and my MBA temp will go over 200F. But closing the high energy tab will cool the it back down to it's normal 115F in minutes. On the plus side, Chrome will sync bookmarks, open tabs, cookies, passwords, and history across ALL my devices.
Safari has become fragmented across 6.1.1 for Lion, 7.0.1 for Mavericks, and 7.01 for iOS. Bookmarks sync between Mavericks and iOS easily but I have to force an update in 6.1.1 by opening the bookmark manager and editing something, then it will sync to iCloud. The Lion version also has a leak in WebProcess that eats all available RAM but it's not consistent. Sometimes it wont hit for days and sometimes it happens on the first page I load. I hate how Safari reloads pages on swipe back but doesn't if I click the back arrow, and how it doesn't open a new tab for highlight and search... I have to remember to always use CMD-click if I want content in a new tab.
Of the 3, Safari has absolutely the worst UI in my opinion. Wide tabs, no favicons in the bookmark bar, and the Bookmark/Reader panel isn't consistent between Lion and Mavericks either. Safari also seems to store bookmark favicons in it's cache... if I reset Safari, all the bookmark favicons are reset too. Apple should make these features app-centric rather than tying them to shared processes central to the OS.
The best feature Chrome and Firefox have over Safari is consistency. Chrome is Chrome, whether on Windows, Linux, OS X, or ChromeOS.