One the Rabid Dog, one the Black Cloud Cat, there's no need to think too much about which one to choose...
At first, Leo didn't intend to sell the information about the Black Cloud Cat, but planned to wait a bit longer.
However, when the Spirit Summoning Guild and the Pale Blue Guild both came to him, Leo suddenly thought of the Black Cloud Cat.
Frankly speaking, it would have been enough to buy the information about the Rabid Dog for 5 million, and the Pale Blue Guild's offer of 10 million was somewhat unreasonable.
Moreover, Leo initially thought that the Spirit Summoning Guild wouldn't be able to compete with the Pale Blue Guild financially, and if they left, he would lose a deal.
So it's better to do both deals at once and sell the Spirit Summoning Guild a favor.
The foolish Spirit Summoning Guild thought they got a bargain, but in fact, they ended up owing Leo a favor.