Tip down ONLY (clip attached to the pivot end of the knife). I will not build a folder with a tip up carry, for two reasons, Safety and Liability. To explain, it is without a doubt the biggest liability position a knifemaker could put themselves into....several makers have gotten themselves into serious trouble by selling folders set up for tip up carry. Again, to explain, with some jarring around, it is very possible for the tip to slightly expose itself inside the pocket, then when it's withdrawn, the tip catches the inside of the pocket, and generally winds up going into the thigh/hip of the person.
How do I know? It happened to me. I was working cattle at a local ranch, and had a tip up carry folder in my pocket...I had been riding for a while and we had a situation that required a knife fast.....as I was rolling off the horse, I was reaching for my folder...apparently while riding/working, the tip had jarred it's way slightly open, as I tried to jerk the folder out of my pocket, the point caught on the inside of my pocket, opened as it was coming out and into my leg. By the time we got the "wreck" settled down, my right pants leg was soaked in blood. Off to the Doc, and a bunch stitches later, I understood.
I know there are a bunch of makers out there who build all their folders with tip up carry, and I know it will offend some of them, but I think that building tip up carry folders is about he dumbest thing a knifemaker can do to themselves. It's an accident or lawsuit waiting to happen. Why put yourself in that position?