The Ubuntu image has been actively maintained for a while now. Though now the maintainer is putting more effort towards Android 7.1. Which is the crux of the issue... These distros are usually maintained by just one community developer.
If you need multimedia and heavy web browsing, run Android. That's what it was designed for.
[1]: http://wiki.pine64.org/index.php/Pine_A64_Software_Release
I'd recommend the Xenial images. There are Mate/i3wm versions for the pinebook, but all the others (Pine64 & Sopine) are headless and require the installation of a GUI.
Then to enable Mali support (which basically lets the device actually use the GPU to render the screen), you have to add an additional repository:
- apt-add-repository ppa:ayufan/pine64-ppa -y
- apt-get install xserver-xorg-video-armsoc-sunxi libmali-sunxi-utgard0-r6p0
then you'd run the script to enable it. Probably need root to run it. - exec /usr/local/sbin/pine64_enable_sunxidrm.sh
Then in your GUI's settings, you'd disable software compositing (force it to use the Mali GPU instead of the pine's CPU) - System -> Preferences -> Look and Feel -> Windows and disable Enable software compositing.
If things go awry, or you have more questions, there's a community IRC that's usually pretty active with people willing to help. http://pine64.xyz/