This is a topic I'm really passionate about as an Leo. I believe one of the biggest considerations should be accessibility to your weak hand. In a worst case scenario on my back and I've rolled on my gun to protect it from being taken can I get to my back up with my weak hand? I carried in an ankle holster for a while and the answer was no to this question. My solution has been weak side cargo pocket carry. It allows for a decent sized gun to be easily concealed and still has a fairly quick draw