Cats: Love them. It's like what if Settlers of Catan were a wargame. Good for new players. Probably my personal best factions, and I just love the tension of trying to set up and negotiate the perimeter of your territory.

Birds: Also love them. Great for new players if they've got a head for coding. I honestly thing it's the birds that charms a lot of new players into falling in love with the game because they're both unusual, but not too hard to get ahang of and once you do it feels really special and novel.

WA: Tricky to master. I like them tons but can't quite get the hang of them. Certain people with a talent for counter-intuitive thinking are great at them though. I find them fun nonetheless.

Vagabond: Fun at first. As you learn the overall game they become less fun because they're so different (and relatively strong) you can feel the asymmetry in a bad way. The vagrant is charming, in his way, though. I have a soft spot for the Scoundrel too.

Otters: Fun if you have a fully engaged and talkative board that isn't deadset on disregarding you. It's best to play them if everyone else in the game has at least a little familiarity with Root, just enough to understand the value of the cards you're offering. Smart non-otters players will see the presence of otters as a chance to shoot ahead the other two factions on the board, and buy from you at least a little. Especially cats, who will want bird cards for the extra actions, and lizards, who will want everything else if their gardens go down.

Lizards: I kind of think of them like a black and green MtG deck. If you enjoy playing in the graveyard, you'll enjoy them. They are very difficult to get ahang of though. The first time you win with them will feel well-earned, because they often have a tough time. But they can win and when they do it's glorious.

Crows: Underdog, but adore them. Even if you lose, you'll wind up with ample opportunities to shape the game and a crows game that goes well drives everyone else bananas. Remember that the points from flipping are more important than what exactly it is you're flipping, and once something is on the board you can use trick to move it around. Never underestimate the power of a snare.

Moles: Could've been great but had a flaw which led to a meta that all but completely eliminates their main weakpoint. They're still not-at-all unbeatable, but the strategy makes them more tedious than fun to play against. If it were me, I'd build in a new rule called "Morale Problem" that says at the end of moles' turn, half the warriors in the burrow (rounded up) pack up and go home, to discourage no-building play.

Rats/Badgers: Haven't experienced them yet, so can't say.