Rimsky-Korsakov's Book on Harmony or Tchaikovsky's Book on Harmony

Not sure if this should be posted in the Theory forum or not, but I figured more might see it here. Anyways, I was just curious if anyone has read either one of these, and what their take on it was. (Not it's Rimsky-Korsakov's "Practical Manual of Harmony," not "Principles of Orchestration"). And I'm particularly curious if anyone has read both, and if you can tell me what makes them different, which they prefer, and why? Thanks.