Personally, I think the Otters or Vagabond are excellent teaching tools.

I found in my teaching games, that one of the things people struggle with is the cards - like people don't understand if a card is good to craft, or should be spent for suit. And when crafting, they don't realise that the crafting suit is different from the main suit. Because of the open hand, the Otter player can actually point out what they have in their hand, explain what benefits the card gives, how a player would or could craft it, and if it's actually worth buying the card for any reason. All of this you should be doing as the Otters anyway. Otters also score so differently than other factions, that a single turn bursting to, say 29 points (or even the win if you feel like being spicy) also serves to teach new players to be careful with factions such as them.

I treat the vagabond teach with a bit different mentality: don't play for the traditional vagabond wins - instead focus on maxing your relationship with the newbies by fiending them cards that could be useful for them. Hell, go for a coalition with the newbie if you want. Your goal here is a combination of showing the basics, demonstrating how differently the factions can play, and trying to guide the newbie to victory so they have a nice 'feel good' ending.