I think really it depends on the knife and the user.
For example, as Powernoodle mentioned, with tip-up carry of a spydie (delica or endura in my case) my thumb naturally ends up on the spydie hole during and after the draw. You don't have to reposition your grip at all to open and properly grasp the knife. But a larger/bulkier folder like my ZT0200 requires tip-down carry; it's the only way I can carry that folder that requires minimal repositioning of my grip after the draw. I switched it to tip-up carry once, and quickly discovered the shape and size of the ZT0200 caused me to have to reposition my grip on the knife every time I drew it.
Furthermore, even though I can carry my delica tip-down, drawing with my thumb pointing towards the front of my body isn't as natural/quick/secure for me as drawing with my thumb pointing towards the back of the pocket, if that makes any sense (the way I draw with a tip-up delica).
As others have said, unless it's a emerson opener, it comes down to preference.