Thanks for your answer.
As you can see the head is completely selected but the orange disappears in some areas.
When I worked on the demon and some of its props this problem has been even worse, but there are objects like the skull that give me just a flickering effect.
That's what happens with the regular selection, but if I use a modifier like 'reduce' as you can see the color becomes solid.
About the smooth boundaries, what I meant was that it's very useful to smooth the selections but when making decorations or if you want to extract/extrude forms you can't use it if you want to have sharp hard corners. As I show in the image you can add polygons to get a decent result, but it's not always possible to use this workaround and anyway it's not an all purpose solution (the angle will never be sharp no matter what you do). In some cases you can use boolean subtraction but even that solution isn't always possible or it could need more work than it's worth.
Having the chance to define how hard the value should be just on custom defined points of the smoothed selection to have sharp hard corners would be great.
Thanks again for your hard work.