I use either a level 1 or level 3 holster depending on how I'm dressing or where I'm going that day. My carry gun is a Ruger P89. Not alot of decent duty holster available for this model but I've found what works for me.
For a "lower profile" carry I use a Bianchi Black Widow belt slide holster like seen here-
http://www.opticsplanet.com/bianchi-black-widow-holsters-for-ruger-sp101-375-size-08.html . I've worn the gun in this holster and had people not even notice it. It's retention is a simple snap strap and thats all.
For my "full on" pistol belt carry where I'm carrying all my stuff and don't care if noticed or not I have a Uncle Mikes Pro3 triple retention duty holster which rides on an Uncle Mikes pistol belt with a spare mag case which holds a spare mag and a led flashlight, my radio carrier for my portable ham radio, and my celphone case. The Pro3, as seen here-
http://policelink.monster.com/products/products/597-uncle-mikes-pro-3-duty-holster , holds my P89 by way of a retention tightening screw, a top strap and a internal hook which grabs and holds the trigger guard until the gun is drawn.
Of course, none of this built in retention or lack thereof takes away the responsibility I have to train in retention skills and I have. The holster is only a part of the plan. The fact is if anyone is going to carry a firearm their should take some retention training and learn how to defend their gun.