i am a serious fan of Paddle holsters for everything including casual CCW, discreet CCW, light escort duty, teaching and range use. besides being easy to put on, they are unrestricted as to their position on the belt.
i use the Fobus paddle for casual carry. usually back and forth to work where i need the easy on and off feature. i have them for Sigs, Glocks, HK USP, Walther P99, S&W K/L-frame and J-frame. they usually conceal under an unbuttoned work shirt.
at about the same level of concealability would be a Safariland 6358 Level II for a 1911. the block that locks into the ejection port offers enough retention to be very secure and yet allows a fast and natural draw
for more discreet carry, i have a couple of Comp-Tac Adjustable Cant paddles for my 220/226. they ride high on the belt and pull the gun butt tight into the body. it allows a very fast draw and retention is via fit...as on leather holsters.
i use a Blackhawk CQC Serpa paddle holster for teaching. it isn't as much a concealment holster as it is a belt holster with a paddle attachment. is very secure with the most natural release and allows an extremely fast draw. i might throw a hoodie over it after a day in class and go to dinner, but it is pushing the boundaries of concealment.