Which NPC do you like most in the game and why?

At this point, none really jumps out. Usually NPCs that appear throughout the entire game with significance to each saga (e.g. Ashfall saga, Doomwood saga, etc.) are memorable, but there's not really an NPC like that. Even the main villain, Vane, is uneventful, especially since he doesn't even show up much even though he's supposed to be a main villain. In other words, there aren't really NPCs that carry from one major story to the next; for instance, you help Galanoth in Ashfall, but he doesn't join your expedition to other places like Lolosia or Arcangrove, so he's just bound to Ashfall. So that NPC becomes comparable to other story-bound NPCs because they generally have a tantamount role for a specific saga.

The way I categorize NPCs, there are story-bound NPCs (e.g. Artix in Doomwood, Robina in Greenguard, Capt. Rhubarb in Lolosia, Galanoth in Ashfall, etc.), then there are minor NPCs, or NPCs that exist just to exist (e.g. give quests, allow access to shops, etc.), then there are recurring NPCs, or NPCs that appear throughout your entire journey (e.g. deuteragonist or partner characters, recurring villains, recurring heroes, etc.).

Personally, I'd like to see recurring characters. But I think one of the flaws with some of the game's recurring characters is that they appear only for specific purposes, rather than something significant to the game's plot. For instance, you might have Artix as the main NPC in the entire Doomwood saga for the plot, but then he shows up as a minor NPC in other places (e.g. a shopkeeper NPC during Frostval to give out New Year items, or something along those lines). When AE reuses NPCs, they tend to use them for minor roles rather than repurposing those NPCs for larger roles, and it oftentimes feels like reused assets of NPCs become a waste.

 

I think it would be interesting to see a roaming NPC that could appear at a random area in the game at any given time. Instead of being a random mob, he could be a friendly NPC that gives out a quest. Maybe that quest could involve finding another random roaming NPC (RRNPC?)

As far as my favorite NPC, I don't think I have one. They all seem about the same to me.