It sort of depends on what really fascinates you, right? I'll avoid naming some of the most popular ones, because it's likely that you've already tried them. If you haven't, I'd really recommend giving them a try. Many people seem to really love them.
In terms of defaults:
I've heard really good things about Solus, and its use of AppArmor seems really cool. Never touched its package manager, so I won't recommend it, but it might be worth checking out. Its desktop environment is really snappy and has an interesting design philosophy.
Elementary is really cool as a boutique distribution; I don't personally feel any urge to use it seriously (I dislike apt as a package manager), but I always keep its live environment on a flash drive, because it works without any setup on basically anything I throw it at, painlessly, and without error. It's got a cool indie app store full of curated Elementary-centric free software, and overall just feels great. Using it, you'll probably notice a few areas that it clones Mac on, and a few that feel delightfully different.
Clear Linux (Intel's desktop distribution) is pretty popular right now because of how simple it is & how Intel seems to be going to great lengths to optimize it and make it a serious contender, but I don't like its desktop environment (vanilla GNOME 3 as far as I'm aware) all that much.
ChromiumOS is probably the best-designed desktop operating system on the planet right now technically, and I say that as a person who really hates Google. UI-wise it's so-so, but UX-wise it's really something special.
But more interesting are desktop environments in general, since they can be used with any variant of Linux you feel the urge to use. There's an exception there, though, in that Elementary's DE and Deepin's DE tend to not work so well or nicely on platforms that aren't Elementary or Deepin.
There are modern environments:
Plasma has hands-down the best UX of any sort of desktop operating system assuming you've got an Android smartphone; you say you're coming from Apple's environment, so imagine the interop between your Mac and your iPhone, but going both ways instead of just Mac -> iPhone. Texting, handling calls, taking advantage of the computing resources of connected devices, using your phone as an extra trackpad, notifications, unlocking your PC, painless file-sharing, pretty much anything you'd like. There are a bunch of distributions that ship with Plasma by default.
Solus's Budgie is kind of neat in that it takes the main benefit of GNOME 3 (ecosystem) with far fewer downsides.
There are also retro environments, if those are your thing. There's a pretty much perfect NeXTSTEP clone (including the programming environment, not just the UI), amiwm is still pretty interesting, there are clones of basically every UNIX UI under the sun, so on.
I'm not the best person to answer your question, because for the most part I don't go out of my way to use new desktop environments and distributions, and nothing above is my first choice. (In terms of window management, I usually stick with 9wm & E just because I have ridiculous ADHD and 9wm forces me to focus while E allows me to tile painlessly if I ever need it. I use three distributions overall, none of which are very popular at the moment, pretty much solely because I'm really picky with package managers & design philosophies.) That's a "me" issue rather than a Linux issue, though.