Emby Theater has come a long way in a short amount of time, but for me, Ember is still the best way to stream on Windows devices (Windows 10 tablets and phones, in particular). It's a more intuitive UX for the smaller form-factors, to be sure, but it also has that smoother native-app look and feel. And ever since Luke, et al. went all-in on "material," I've enjoyed Ember even more for sticking w/ Windows 8.x/10's design languages.
Also, as far as I know it is still the only client app on Windows that works w/ Emby's sync capabilities. You can create and manage jobs from within the app. It even let's you select the local storage location for synced files, which is particularly useful on mobile devices with limited built-in storage (you can relocate your synced files on a microSD card, for example). It's really stable, even on low-end systems, so I got this $50 beater of a tablet and a $10 microSD card, and loaded it up w/ synced movies and TV shows for my kids on road trips.
If you're using Windows devices for streaming, I highly recommend springing for Ember. 7illusions is good people.