What I would say is that I chose Solus because it was easy. A lot of other distros out there require a bit more finagling around to get things working just right. I had this problem a little bit with Manjaro (the first distro I used for any significant length of time), and it's a big part of why I left Manjaro and went to Solus. Now as far as the other easy distros out there, distros like Linux Mint, or Ubuntu Mate, most of them are not rolling release. Meaning their software may or may not be as up to date as Solus. They may have more options to choose from in terms of applications you want to use, but many of them will be redundant, and as I just said they may or may not be as up to date as what you get with Solus. The main advantage of Solus over it's competitors is that it offers a small stable and up to date repository of software, while other distros either tend to offer large up to date unstable repositories, or large not up to date stable ones. Solus strikes the balance giving just the amount of software you need whilst maintaining stability and frequency of updates.
As for what Desktop environment? The one with the most customization options is KDE Plasma. However, if you are new to Linux I would give you a word of caution about Plasma. The Plasma iso still isn't an official version of Solus yet. It's currently still considered testing. Further KDE (in my experience) tends to have more releases that can be a bit wonky than the gtk based environments. If you go with KDE you may, on rare occasions, be faced with an odd bug or two that you have to deal with. I don't mean to dissuade you. I use KDE Plasma on my main pc right now, and I love it. It's great. It's just that occasionally it will give me a problem I have to deal with. For example, for the past little while Kmail (the default mail client if you use KDE) hasn't wanted to work properly with my Gmail. There was once a long time ago that a KDE update got pushed that somehow managed to bork half the KDE applications on my computer. These things happen rarely, not enough that it's bothered me, but your mileage may vary. I'd say KDE is overall a more complete, but a slightly less smooth experience than some of the other desktop environment options.
Both the Budgie, and Mate environments are relatively easy to customize (using Gnome Tweaks, and Mate Tweaks software respectively), and will give you a bit of a smoother simpler experience. So if that's what you're looking for then I'd try one or both of them out. I personally run a distro called Debian using Mate on my laptop so I can vouch that Mate is very very good. I also used to use Budgie a long time ago, back when I first started using Solus. It was really good then already, and from what I've heard it's only improved since. Both of these are easily customizable and easy to use. They may not have the sheer girth of options KDE offers, but they get the job done.
The Final option would be GNOME I don't know that I would recommend this to new Linux users or not not. It can be a bit finicky to customize, and it's a completely different desktop paradigm from any other environment I know of. It is very unlike windows, and I'm not even sure it's that similar to Mac. Only use GNOME if you're looking for something completely different then you're likely used to. I used GNOME for a few months before switching to KDE early this past year. It was enjoyable, interesting, and elegant. However there was a slight learning curve due to it's different paradigm of use. I had a few issues with it being a little slugglish, but I've heard that these have recently been resolved. Gnome is good, but strange, worth trying out, but very different from the others. Also it's probably the least customizable .
Honestly I would advise downloading all 4 versions of Solus, and then trying each of them out in turn. You can do this by just running them off a usb stick. You have to do this before you install anyways. when you plug the usb stick with the solus iso on it into a usb port and select it to boot from when you turn on your computer you will be taken to a live environment where you can try it out before you choose to install. It will likely be running a little more sluggishly like this then it would once you install it, but it would be good enough to get the feel for which environment you'd feel most comfortable with. Also keep in mind that people on these forums (as far as I can tell) tend to be eager to help each other out so if you run into any roadblocks when installing or afterwards never be afraid to post here, or even over on the reddit page for help π