I did a lot of breeding and poaching of my own monsters, so I used Mediators a lot. In addition there are several points like learning Zodiac and finding rare treasure with Move-Find where lowering Faith or Brave came in handy.
Reis is underutilized unless you have at least one Dragon ally, but I found my favorite monsters in battle were Tiamats: flight, three way attacks, insane physical power, plus a long range (if random) attack.