This is part of a Silvan fellowship featuring Dori, intending to set up a Dori-assisted prime defender. The ideal choice would be Celeborn, since he is already noble and can get sentinel with Elven Mail, making the Heir of Mardil/The Day's Rising combo possible. For added goodness, you can put Light of Valinor on him, Song of Wisdom and A Burning Brand. Add Steward of Gondor and Gondorian Shield and he becomes an all-around awesome defender. Heck, slap the Cloak of Lórien on him while you're at it.
However, that takes a lot of attachments, and both his hero compatriots also can defend for 4 with Dori's help, and have some good arguments for being a prime defender. Prince Imrahil can be readied once by the many return-to-hand events, defends for 4 on his own with a Gondorian Shield, and as a noble can be readied by Heir of Mardil comboed with Steward or Errand-rider. Armored Destrier is especially good on him as well, since he has the highest base attack. Beravor isn't noble, but her special ability makes her a logical defender -- with Wingfoot she can quest and ready if needed, and if not needed for defense can always draw cards.
So the bottom line is that the prime defender's identity on what attachments come out in what order, and may shift during the game. With Dori's help, all options are solid defensively.
All the hero attachments reduce the density of silvan allies in the deck, which is what you'd expect a Silvan deck to normally be about. However, there's enough that The Tree People usually hits, and the deck should build up decent questing and even combat over time.
In the sideboard, Son of Arnor is for engagement problems, Thror's Map for travel problems, Athelas for conditions, Expert Trackers for location heavy, and a third Feigned Voices for enemy heavy. Even with decent defense, readying Imrahil and getting another first-turn-ally boost can be helpful.