I have both a 5S and a Note 3. The Note 3 came first, and the reason I bought a 5S was because I have an iMac desktop and Android doesn't play nicely with OS X; I find the OS X Android File Transfer app awkward and unreliable.
So I bought a 5S, and yes the integration with OS X is better. But the reason I've gone back to the Note 3 (whether temporarily or permanently I don't know) is because I just find the 5S screen too small. I do a lot of web browsing, ebook reading and emailing, and I find the 5S screen just isn't in the same league as the Note 3's, which just makes me feel good every time I look at it - especially with a nice wallpaper. I also find the 5S's on-screen keyboard too fiddly, whereas the Note's is a joy to use and - a big plus - has letters and numbers on the same screen. The Samsung will also 'learn' your written style and make intelligent predictions of the word you want. If you want to do that on the iPhone, you need to use SwiftKey (or similar) and then, because iOS SwifytKey for some bizarre reason produces an (unalterable) large font, you have to sync with Evernote and then copy and paste into Mail. The Note 3 does it directly in your email app.
The Note has 4.4 Kit Kat, which I find excellent - quick and smooth, and in my experience just as good as iOS 7.1. It will also multi-task - you can set up multiple windows on the screen. Android will give you widgets (iOS won't), which I find very useful and allow you to customize the screens in an aesthetically pleasing way.
As regards syncing with the iMac, I've now turned the Mac into a dual boot machine with Ubuntu as the second OS - problem solved; you can transfer files just as easily as you can with Windows.
Downsides of the Note are that the build quality is not as good as the iPhone (though in practice I can't say this is a problem for me), and obviously it feels bigger in the pocket. But for me, for now anyway, the pros outweigh the cons.
Hope this helps.