I finally did an experiment with all options
The top row is using Whisper White CRAFT ink and the bottom row is using versamark.
Here is the detailed breakdown of my experiment:
WHITE EMBOSSING POWDER
I was told, years ago, that using Whisper White Craft ink as the base of your embossing, you would get a 'deeper' white, but after this experiment, I really didn't see a huge difference. So if you are not planning on doing a chalkboard effect stamping, I would not bother buying the craft ink.
On a trip back on memory lane, Stampin'Up! used to have ALL their inks also in craft version. That is when they only had clear embossing powder. So the only way to get different coloured embossing, was to use a coloured craft ink. And if you read further, you can see that the results using coloured ink and clear embossing powder were not super great. I have to say, it was not so bad when using white card stock. For example stamping with Real Red craft ink and clear embossing powder on white card stock, the result was not as bad as on this black card stock.
Here are detailed images of the white embossing powder samples
As you can see, I didn't use my embossing buddy, that is why there are those white smudges around the image. I could say that I did it so that you can see what happens when you don't use the embossing buddy, but really I was just too lazy :-)
CLEAR EMBOSSING POWDER
This is using versamark and clear embossing powder. As you can see, it gives just a shiny surface.
Where this is very useful is if you want for example a shiny starry or snowy sky, you could use blue card stock and emboss clear snow flakes or stars with versamark and clear embossing powder.
Another way to use this combo is to do a resist technique. You can stamp an image, either a background stamp (like world map) or a flower stamp, and then rub ink with a sponge over the embossed image. Remember to wipe the surface after inking with a clean dry paper, to remove the ink from the embossed image.
Here is an image of clear embossing powder over Whisper a White CRAFT ink. It makes a chalkboard effect with a shine. Not my favorite look :)
If you want to create a card with chalkboard look, I would recommend using Whisper White CRAFT ink. Just remember to let it dry completely, or use your heat gun to dry the ink. If you want to create a 'poorly wiped chalkboard' background, you can use a dry sponge and smudge Whisper White CRAFT ink over the black card stock.
EMBOSSING WITH VERSAMARK
These are same images, but just from a point of view using same embossing base with different embossing powders
Here is a comparison using Whisper White CRAFT ink without embossing and embossing it with clear embossing powder