The most legible text layout, in theory, is ragged-right black on white. But you need legibility in practice, rather than according to a theoretical ideal.
The eye loves white space.
Upside-down text is hard to read.
Cross-references are reader torture. Put all the information required in the same place, even if it means repeating it.
If you refer to a previous graphic, reproduce it - only smaller.
Tiny text which might be OK for a short label would be quite illegible for any length of text.
Gridlines for graphs are helpful but should defer to data lines.
Eye candy is OK in small doses. Decoration should defer to meaning.
Data labels should be minimal and as precise as possible.
Establish layout rules for clarity, break them for interest.