Historically it was a preferred form of capital punishment, but these days there's a negative stigma with decapitation as a barbaric method of execution that's often used by terrorists like ISIL. I've read observations which say that the head may remain conscious for a short while, but death by guillotine still seems like a less painful death than hanging,electrocution by the electric chair or from what I've read lethal injection as well, all which are more common.
I know that the last execution by guillotine in France was in 1971, and they only stopped due to the banning of capital punishment. France continued to execute people by guillotine in public until 1939. There is actually a video of that execution, but it is from behind and from a distance.