I'm a big fan of Agustria, but mainly the northern section you visit in chapter 3. I just really like how the area feels alive with villages, as well as the Orgahill stronghold and Blaggi Tower area having a nice aesthetic.
As for least favorite, that's gotta be Silesse. I already typically dislike snowy areas because they feel stale to me, but it Silesse feels so shoehorned into Jugdral compared to the other areas. Nothing of note really happens in Silesse in either generation imo.