I own both types and carry both types.
I find that for small knives the speed of deploy is about the same but for larger knives tip down is much faster. I've done experiments with both and when pulling a large knife, even with my long fingers, my thumb is several inches from the thumb hole. Even with medium size knives I got in the habit of pulling the knife out, tossing it up in the air and catching it flipped around and then I can open it. It works well enough in normal use but is not 100% secure. A large knife carried tip down has the thumb hole right at my thumb when I draw it. Also I typically wear tight jeans and that makes a difference. I've seen videos of people quickly deploying large knives while wearing pajamas, but I don't own any pajamas and even if I did I couldn't wear them out of the house.
I have had folders open twice accidentally while handling them, they were older folders that had essentially no detent. My modern folders with detent have no problem with accidentally opening so I don't worry about carrying tip down. There are stories of knives opening in pockets and cutting clothing and/or flesh, some people are conservative and wish to carry their knives with the blade against the edge of the pocket to keep it from opening. Other reasons for tip up are to use a wave opener or to carry a knife with a lanyard. Not everybody cares about speed of deploy, even people that prefer tip up sometimes admit that this slows down the deploy of something like a military.
So there are lots of reasons for carrying one way or the other. Everybody is free to do as they please and there are plenty of good knives made each way. You will find that in polls like this something like at least 3/4 of the responders prefer tip up.
I find that for small knives the speed of deploy is about the same but for larger knives tip down is much faster. I've done experiments with both and when pulling a large knife, even with my long fingers, my thumb is several inches from the thumb hole. Even with medium size knives I got in the habit of pulling the knife out, tossing it up in the air and catching it flipped around and then I can open it. It works well enough in normal use but is not 100% secure. A large knife carried tip down has the thumb hole right at my thumb when I draw it. Also I typically wear tight jeans and that makes a difference. I've seen videos of people quickly deploying large knives while wearing pajamas, but I don't own any pajamas and even if I did I couldn't wear them out of the house.
I have had folders open twice accidentally while handling them, they were older folders that had essentially no detent. My modern folders with detent have no problem with accidentally opening so I don't worry about carrying tip down. There are stories of knives opening in pockets and cutting clothing and/or flesh, some people are conservative and wish to carry their knives with the blade against the edge of the pocket to keep it from opening. Other reasons for tip up are to use a wave opener or to carry a knife with a lanyard. Not everybody cares about speed of deploy, even people that prefer tip up sometimes admit that this slows down the deploy of something like a military.
So there are lots of reasons for carrying one way or the other. Everybody is free to do as they please and there are plenty of good knives made each way. You will find that in polls like this something like at least 3/4 of the responders prefer tip up.