Someone asked what regions the Crests are more 'commonly' found:

Faerghus: Blaiddyd (royal family), Dominic, Fraldarius, Gautier, Daphnel (from House Galatea), Aubin and Timotheos (extremely rare)
Adrestia: Seiros (royal family), Lamine, Charon, Macuil, Indech, Cihol, Cethleann, Noa (extremely rare)
Leicester: Riegan, Gloucester, Goneril, Daphnel (the original branch), Chevalier (extremely rare)

There's also the Crest of Ernest, but it belonged to a DLC character and there's no real information on it. So I guess anywhere?