I can honestly say I like serpa's level 3 for retention. Dont like retention too much though... I can get anyones firearm out of their retention holster just as fast as a normal holster so I dont see the point personally. Actually with a retention holster it seems easier to me to steal guns off the sides of my friends when teaching them actual weapon retention skills 
"Go in there! Get something done! And if you die, die the F***ing hero! I am sick of these internet warriors saying 'oh well I'm not going to protect them.. I'm just worried about me and my family'... F*** YOU!" - James Yeager
