The best home defense gun is going to be different for each one of us. As an approach to finding the answer that is best for you, I suggest starting with all options on the table and then using a process of elimination based upon your specific needs, your physical ability, and what type of gun you might actually like to take to the range.
You MAY NOT shoot at a fleeing suspect unless that individual is presenting an immediate threat of death or great bodily harm as he flees.  In plain English, if he’s not trying to kill you or somebody else, you cannot use deadly force to stop him from getting away. 
While the average American citizen might make the assumption that CPR and first aid basics are only required in emergency services positions, the truth is that understanding these techniques are extremely important in any line of work.
The mode of carry is going to be a comfort issue if you hike any distance. I have hunted for many years and had many friends carry side-arms in holsters that work fine while sitting in the car, at the desk or walking around the mall.  However, they have been extremely unhappy and uncomfortable after getting four or five miles back into rough country in the heat, cold or whatever.
“What does that mean for me and how can I make more money as a security guard?”  The answer is simple and has three parts: experience, training and focus.  Let's take them one at a time.