My first two daily carry knives (that had a clip on them and weren't just "tradional pocket knives") were a BM mini AFCK, and a BM Ascent 830. Although the 830 has a clip that can be switched from tip down to tip up, I carried it tip down, which is how it came out of the box. Several months later I bought an Endura which is only tip up. I tried to carry the Endura the first day, and I had so much trouble remembering how to position my hand to grab it that I just never carried it. After practicing with both for a long time, and reading posts from everyone here, I have come to the conclusion that it just depends on what you get used to. It appears that many of you can draw and open a tip up blade just as fast as I can draw a tip down blade. Quick-draw is not that important to me, but when I grab my knife out of reflex or when I'm in a hurry, I resort back to my most natural hand position, which is to always grab tip down. Plus, it can be hard to remember which knife you are carrying if you switch often from tip down to tip up. I have recently tried carrying my Endura on my left side (with the clip still oriented for right-hand opening) and grab it with my right hand in a cross draw sort of motion. I find that this works very well in that my hand naturally draws the Endura in a way that is quick for me to open because I naturally give the handle a spin (from butt to tip) before opnening, so it opens easily for me. Furthermore, my Endura is pretty easy for me to open left handed even with the clip on the right hand side, if for any reason I needed to open it with my left hand. Because I'm right handed I will naturally grab my knife that is at my right if I need it quickly or react out of reflex, so I don't have to worry because I am used to opening the tip down one and it's the fastest for me.
Sorry this got so long, and that I didn't explain myself very well, but to answer your question, now that I'm used to this configuration, I will always carry a tip down on my right and a tip up on my left. I think my reason is just because that's what I have gotten used to.