Me, I normally go for looks.. Maybe since I have a back ground as a
calligrapher and to a degree paleographics. The letters should look
good together, as well as no blend into each other, basically legible.
What goes for a block letter form, when turned into cursive it can
quickly become hard to read. Or just does not flow into each other.
Looking like a mass mess of letters.. Unless you are going for some
form of Court Hand that was designed to not be read but by the
initiated in its forms..
Tengwar done by Tolkien, seems to have some logic to it. Voiced and
Unvoiced, Palatal and Dental and like.