Less and less do I profess my favorites, as when I do somebody says I'm all wet because their favorite is somehow superior. Good for them. And that's why we have choices.
But in this case I'll break my rule, and I will absolutely endorse the Bianchi 5B series of holsters for the Security Six. They are simple, well made, high riding and with the correct belt, hug your body very tight.
I've got many, maybe even dozens of holster choices, and this model of Bianchi remains my favorite for Security/Speed Six revolvers.