Squirrels are not necessarily harder to kill than most other critters but they are very, very difficult to kill quickly. Since squirrels have the ability to climb trees and get out of reach, and are smaller than most other game animals we hunt and harder to find even on the ground after hit, it is important to find a way to kill them quickly.
I don’t know what is the absolute best head to use as I haven’t tried everything out there. I’m always looking for the “best”, but of the heads I have used by far the best is the bladed blunt. It produces both the shock of the blunt with the penetration and cutting ability of a broadhead. Keeping the arrow in the squirrel after a hit greatly reduces the chance of a squirrel being able to get back up a tree before he dies, or before you can get to him after he has been able to hide on the ground. Too many times a broadhead alone will pass through, and the steel blunt alone will not always penetrate enough to stay in the squirrel.
A squirrel hard hit with about any head will die, many times a slow and painful death if you can’t get to him and find him quickly. The goal is to be able to retrieve the squirrel, and do so as quickly and humanely as possible. Head shots of course are ideal, and in this case type of head used is irrelevant. I can’t even come close to getting 100% head shots so type of head used is important to me.