Liquid is most powerful being pure power and having the most uses. Solid is the least powerful with only one specific purpose. gas is the middle ground.
Example (allomantic): lerasium (solid) turns people into mistborn, the mist can replace metal as a fuel source, and the well of ascension can drasticly change the landscape.
Some more information for you.
Only people with the correct physical spiritual and cognitive genetics can use retain types of magic. e.x. Only people from Scadrial can use Allomancy.
I was trying to say how we don't know enough to make a textbook of it. And remember, Vasher was one of the Five Scholars.
Also, breath is not someones soul, that was the argument of anti-awakeners.
Personally, I believe that Breath is a part of Endowment and only happens to appear within Humans.
I apologize, I have been known among my friends as taking things too literally.
If 17th Shard has more than one goal, there is also the possibility that 17th Shard isn't unified.
Personaly, I think that BioChroma is the most useful of all the magic systems, since anyone can use it without any specific genetics, change or prior interference. Provided you have Breath of course.
As to a textbook of sorts, I don't think BioChroma is complex enough for it. You can easily explain how Biochroma works in a paragraph.
Since it was theorized that 17th shard uses shadesmar like HOID I tried to make a shadesmar version of Sel.
Unfortunately I am not much of an artist...nor do I know how to post images.
could someone tell me how to post an image?
Then I put up my version of shadesmar Sel.