I know it is a little early, but unfortunately we already have clear winners and it is very unlikely to during the rest of the year. In 2015 I wrote about the desktop Linux being in a state of boredomness. Not much has changed in two years, but there are some interesting developments.
The best for productivity and overall: Ubuntu 16.04 LTS
While Canonical seems to be lost with their Unity 8 project and the version 7 has some irritating design decisions, it just works. The recently released 16.04.2 brings the hardware enablement stack, which means that you are running a fairly current Linux 4.8 kernel and graphics stack. And new releases are expected on August 2017 and February 2018.
Productivity does not necessarily mean business use. It means that you can use the system without interruptions and less time spent on system administration. This is desireable for workstations, but also if you are using our computer as a media player/streamer - you don't want to tinker with your PC, when it's time to Netflix and chill.
The best for hobbyists and tinkerers: Manjaro Linux
I have written a lot about Manjaro. It is a fantastic Arch based rolling release distribution, with leading edge software. It works very well out of the box and you are always current. Recently they added Gnome as an official Manjaro edition, which is a very welcomed addition.
While Manjaro is awesome, it is not a zero maintenance system. Updates are frequent and problems may or will happen. It is ideal for hobbyists and enthusiasts who want to spend time administrating the system. A very active community is there for support.
If you really don't need powerful offline apps, the CloudReady is a great system for surfing the web. It is a fork of Chrome OS open source project. It is light weight and suitable for older hardware. And best of all, it is a zero maintenance system. Release updates are delivered over the network, so you are always current and minimal user interaction is needed for updates.
Your applications are limited to web services, but nowadays you can get quite far with them. Tinkerers can add a full blown Linux inside the system using Crouton. CloudReady is definitely worth a look, and I am loving it on my old Thinkpad.
What did not make it on this list?
I have to comment a couple of distros that I tried, but did not make it here. First one is Fedora 25. Some bloggers have been excited about this release and even crazy enough to recommend it for Linux newcomers. Absolutely do not go for Fedora, unless you know what you are doing. They have tried to make it more useful for generic use, but unfortunately the result is what it has always been: Bleeding edge software with a ton of bugs combined with a frustrating out of the box experience. I tried and installed, and encountered issues I have never seen before on my very compatible hardware. It looks good though, and Gnome on Wayland runs smooth.
Another distro to warn about it OpenSUSE Leap 42.2. They advertise it as an alternative to Ubuntu's LTS releases, saying that Leap combines enterprise quality software packages with more recent updates. Bullshit. They have software quality issues, cumbersome package management, unpleasant out of the box experience and overall it will just drive you crazy. As with Fedora, do not touch OpenSUSE unless you know what you are doing and looking for.