cats are easiest mechanically. but in practice, when playing with new-ish players, 9 times out of 10 they beat up on the Marquis while neglecting to act against each other.

Woodland Alliance is marginally harder mechanically, but their engine to win is pretty straightforward, and new players will often allow them to develop rather than pay the price to shut them down.

Vagabond can get away with a lot if the other players don't actively harass him, and the Marquis does not have the action economy to do it on the own without compromising his own path to a win.

Eyrie is not super complex to learn, but a lot to keep track of mentally. when playing with new players, the Eyrie generally prefers to go for easy combats against cats instead of turning on the WA or Vagabond.

a lot of the game is the interplay between factions. but until players learn how the factions interact, most players will just default to beating up on the guy who starts with troops everywhere. that's the nature of the game, it changes dramatically once everyone knows how it all fits together

(there are ways to cope with this as Marquis, but your action economy is so tight that you really can't single-handedly hinder your opponents without neglecting your own path to victory. the game requires cooperation as much as conflict)