Update:
i decided to add to my previous post and do sum testing..
i have a ducky DK9008G2 Pro with MX grey linear switches and decided to try out all my o-rings.
first row blacks , second reds, third blue..
Because the MX greys i have are linear i had trouble noticing the difference between o-ring types.
The only little thing i noticed was the travel distance being reduced from black to reds to blues.
So i decided to switch the keycaps to my Leopold with MX clears hoping the difference would be better noticeable..
This time i did the same test 3 rows of different o-rings.
Stil i had to focus on my typing to tell the difference...
My conclusion is as follows..
if you want to prevent the clacking noise and feel of bottoming out and prevent the harsh feel of smashing the bottom plate (depends on your style of typing,)
Than the black o-ring would be sufficient.
if you want to ad a bit of couching ,,just a bit mind you ..without sacrificing travel distance i would recommend the reds.
But if you don't mind the travel distance as long as you feel the actuation point and your not gentle with your typing style.
Than i would go with the blue o-ring..
Also the type of switch plays a big part in o-ring choice.
For heavy switches i would recommend blacks or reds..
For lighter switches i would get the blue,,
To be honest i would pass on the black o-rings.. Only if your a purist and just want to be a bit quieter hahahaha..
i'm going to get a third keyboard soon.
The Kul ES-87 with MX clears
https://mechanicalkeyboards.nl/en/shop/product/kul-es-87/
And after this little test i think i will be going for the red o-rings.
Just because i like the feel of the travel distance ..
There are sum people that claim they can type faster with mx-clears and blue o-rings reducing the travel distance and so on...
Hope this helps a bit..