Autoseams addon is good for quick UV unwrap.
It is especially good on chaotic meshes, like scan results, decimated meshes and others, where manual seam selection is slow.
On regular meshes, it produces not-so human likeable islands.
On highpoly meshes, could be extremely slow.
Still, it’s the best auto UV solution in many cases.
It tries to produce islands that are nice in more aspects - shape, deformation, area.
Gpack, gravity packer,
is an experiment, to enable interactive UV packing in blender. Blender only has a box packing solution by now, which is quite bad. I don’t use this in production, but I release this for inspiration.