What is the easiest Linux window manager for people familiar with OSX?

Well that would be gnome. With a little bit of tweaking(gnome tweak tool) , you could easily emulate the OS X feel. Here's my Fedora workstation for comparison…

In case you're wondering, I use the numix-circle icon pack, flat-plat-blue gtk+ theme and adapta-nokto shell theme(gnome-look.org). Also for the dock I used the dash to dock extension(extensions.gnome.org).

As for the keys.. The Mac command key maps to the Super key and the Mac option key maps to the alt key.

Cheers.

XFCE has many similarities. However it’s more similar to earlier Mac OS versions than with current one.

But I think Pantheon desktop that can be found only in Elementary OS (this is another linux distro). I think it’s possible to install this desktop environment in other linux distros too however I haven’t tried. But from other side if is OK for you to work with this distro maybe this could be a good answer.

Gnome like other answers pointed also can be used for Mac OS desktop emulation on linux.

I think is impossible right now to suggest one real winner here. All these options has own minuses and pluses. It would be better idea to try all these options and choice by yourself.

I’d recommend gnome2 if it still existed. But modern day Linux leaves no room for grievances. I don’t recommend you try to make Linux similar to OSX —not because Linux is better, they’re both good in their own ways— you’re much better off staying on an Apple device if you need or like it. I mean, what would you tell a Windows user is the best way to configure Mac to feel more Windows-y? You’d tell them that’s sacrilegious haha. Having said that, Linux is about freedom not some Dogma hehe.

You can try out Elementary OS if you’re really insistent. It looks like OSX. Except it isn’t. So it’d eventually start to wear on you.