CR39 has better chromatic aberration. Higher Abbe number means less aberration. CR39 has the lowest chromatic aberration of any material commonly used to make glasses.
What I couldn't figure out is whether a CR39 lens' comparative thickness (prism length) vs a thinner Trivex lens degrades its chromatic aberration advantage in practice.
http://eclecticeyewearaustin.com/wp-content/uploads/2016/05/...
However, due to the selling point of Trivex being "shatter proof" it has a greater centre thickness (to pass safety lens regulations), and thus the edge thickness is also comparable to CR-39.