* Alpine is lighter-weight. As at least one point, Alpine packages are split into small parts (usually at least app, app-dev, and app-doc, respectively containing the actual program, the development headers, and the manpages/docs). Alpine also defaults to using Busybox for coreutils.
* Void is rolling release with regular updates and a surprisingly large repo. Alpine has a rolling "edge" release and stable releases that are supported for 2 years.
* Void works on a traditional install to a writable root filesystem; Alpine can do that ("sys" install), or can run in RAM, optionally persisting state).
* Alpine uses hardened kernels. They used to use grsec, not sure what code they use now. Additionally, they configure the system to be locked down; for instance, on the laptop I'm using to type this comment, I can only check the battery status as root, and powertop outright doesn't work (as I understand it, they completely killed off the debugfs interface it needs).
* Void seems to be more into cutting-edge tech; ZFS and wireguard come to mind.
In general, Alpine is designed for embedded, Void is a general-purpose system. Both can do the others' job, but that's their tendencies.
my LXC container basically runs up DHCP to get an IP and a SSH server to provide a remote shell, everything else is per-server setup like webservers and stuff, compared to the ubuntu containers I run Alpine uses a LOT less memory and CPU.
I think it's still the recommended way for dependency management reasons and missing glibc-packages. If you can get your program running with the alpine glibc you should probably do that