I believe that Rick has two possible favourite characters.
Rick gave Percy ultimate powers
Percy defeated a whole bunch of titans with a water hurricane, and exploded the toilets on the Argo // without even trying.
Percy has his own series
The Percy Jackson series started me off on the Rick Riordan books, and he was a very powerful demigod, defeating all monsters in his way.
Apollo (God of archery, music and dance, truth and prophecy, healing and diseases, the Sun and poetry):
Apollo has a whole series to himself
Apollo is turned onto a mortal by Zeus, and then betrayed many times, but I think Rick did this so there would be drama, and also because he feels Apollo isn’t really in any of his other books.
Rick gave him lots of funny scenes
There are many funny scenes in ToA, and in the chapters when Apollo is involved in other books, he’s seen as a humorous character. I think Rick favours Apollo, which is why the god is humorous.
Do you think that Rick has another favourite?