I can't help stressing how any BSD is really a viable choice here 😉 ....and on the other hand how none is: no wifi support nor 3D acceleration available but using omxplayer which afaict is available on NetBSD only;
Net is more lightweight on resources, but it's a matter of of few megs 😉
Some more points to take into consideration are tge availability of binary packages and the ease at cross-compiling if needed; I have no expereince with Free or Open in this field, so you'd probably better investigating further.
Oh, one last thing: make your choice also depending on software you're seeking out. i.e. if you're more comfortable with GCC, then NetBSD is the best choice, whereas if yiu prefer a LLVM toolchain, then, by all means, go with Open or Free