Ubuntu: kernel 3.14 vs 4.9

I wanted to know in practice what are the new features introduced with the 4.9 kernel compared to 3.14 if someone has got to test both the kernels I would be grateful

I think the main difference for practical purposes is that the 3.14 builds will have the potential for Android hardware drivers to be ported. This means that graphical hardware acceleration is an option in 3.14.
Since ARM will not release drivers for Linux, there is no option for hardware acceleration within Ubuntu running 4.9 and other hardware is unlikely to get mainline kernel support either.

If you don’t need what 4.9 has to offer then I would stick to 3.14


This is not entirely correct. 4.9 is the next kernel base for Amlogic and (almost) everything that is working in 3.14 should also be working in 4.9, at least for S905X and S912 devices, so for both VIMs. Some things might not be working in the same way as I think Amlogic worked on 3.14 much longer.

When you say “mainline”, you mean 4.16 kernel and indeed there is still a lot to do.