I use the Kernel 4.0.x releases (4.0.2 at the moment) and I'm fully happy with it.|
If you have no experience at compiling and configuring kernels, I agree with tkaiser, then igor's images and scripts are the easiest way to compile the mainline kernel.
If you don't mind compiling on your own, then I think following the linux-sunxi wiki to compile the mainline is sleeker in my opinion. The only caveat here is to find or come up with a configuration that suits your needs (again, igor's config is a good starting point here, though it will contain some stuff you might not actually need). Once you have that, you can automate the kernel compilation and updating with scripts very easily.
I use a set of scripts to check regularily if a new kernel version is available on kernel.org and if yes, automatically compile it and notify me via email. Another script, that I run manually, handles the installation of the kernel and reboot. So updating the kernel only requires me to log in via SSH, issue one command to install the new kernel, and that's it. Even that could be done automatically via cron, but I prefer to choose the installation times myself.