Started with the initial Riders of Rohan Starter Deck, and tweaked it a million times from there. Most noticeably, the deck shifts from heavy to more instead. Théoden replaces Hirgon's ability to play allies for cheap without having to commit him to the quest first, which is very nice. He also plays pretty neutral himself in that he could quest if needed, but also provides a decent attack or defense option. Éomer on the other hand is strictly for attack, and Lothíriel is for questing. When Hirgon was in the deck (for many playthroughs), I felt like all he was contributing was the ally discount, as I was rarely using him for literally anything else.
I feel that overall costs with this deck are pretty low, especially for allies, so that most of Eomer's resources can go towards his war attachments. Guthlaf costs only 1 to play due to his ability combined with Theoden's, which is why I added him x3. Westfold Lancer costs nothing as he will be questing for free with Lothiriel.
My goal was to be able to get more allies in play and usable, which was a weakness of the Starter Deck, combined with lack of card draw. Cheaper allies, x3 Horn of the Mark (necessity), and Foe-hammer seem to improve this. The remaining Event cards come down to personal choice, and was the trickiest to decide. I went with A Test of Will and Feint to add some tactical defense. Stand and Fight again helps with ally flow. What makes me sad to leave out was fun stuff like The Muster of Rohan, Oath of Eorl, Quick Strike, etc.
Lastly, Eomer needs his war-gear in Firefoot and War Axe to be the main attacker. King Theoden has his trusty Herugrim as well when needed. In the future, I plan to add Golden Shield for Theoden when I acquire it. He will then really be an Attack/Defense option!
Additional notable mentions that didn't make the cut and that were difficult to leave out of this build: Snowmane, Riddermark Knight.