Upgrade or alternative upgrade?

People have actively figured out the old situation, and now there's a question, slightly off-topic, but I don't want to create a new thread for just one question; I hope the moderator understands: I always play as the Dwarves, but I can't figure out which ones are better: Erls or Jarls? And secondly, would you mind suggesting which units to upgrade (for each warrior): Warriors, Harpooners, Berserkers, Bears, Priests, Dragons, Tany? I'm having some problems, and I want to make sure I'm upgrading them correctly. I'd like to hear your advice on fighting against the Sylvan faction. And also, which hero should I choose? I usually take Sylvana (I think that's her name), and I'd like to hear your suggestions.
P.S. Please provide arguments with your answers; it will be easier for me (a newbie) to understand.