I have been tinkering with Linux for nearly 20 years. For many years I was a "distro hopper" - trying out different distributions and combinations of desktop environments.
If you want a system which is highly configurable and don't mind doing a bit of extra work to get things the way you want them, go for Arch Linux. The Arch User Repository (AUR) is one of the best I have seen anywhere. Also, there are some more user friendly distros such as Manjaro that are built on Arch.
If you need a rock-solid server, go for Cent OS or Ubuntu Server.
If you want a system that balances good stability with the newest and best open source software, try Fedora.
If you do a lot of office work or system administration, go for OpenSuse.
If you are looking for older stable versions of software, go for Debian. There are developmental branches of Debian if you want to try newer versions.
For newbies and oldbies who want a system that is very well supported, has long and short term releases, good repositories and excellent third party support, go for Ubuntu.
If you are an Mac wannabe who wants a system with plenty of eye candy, go for Deepin or Elementary.
And finally, my view on the desktop environments:
KDE - a very comprehensive and highly configurable environment, but a steep learning curve for some.
GNOME 3 - minimalistic by default, but powerful and configurable 'under the hood'. It's designed to work well on desktops, laptops, tablets and touchscreens. If you prefer the older GNOME 2 style, go for MATE or alternatively use the Gnome 3 "Classic Session"
XFCE - fully featured environment which runs particularly well on older hardware.
Cinnamon - great for people making the transition from Windows.