I've always had difficulty putting together a Rohan deck I was happy with. The classic / can have issues with defence and card draw, while going / instead means missing out on some of the good attack power which can be considered a strength of the trait. So I figured, why not go tri-sphere? With Théoden's discount I can still afford my allies, helped along by Théodred passing resource around, I get from in Snowbourn Scouts and Wardens of Helm's Deep, from Éomer, Firefoot and Westfold Outriders, plus Herugrim, and decent questing from .
This deck can be a bit slow questing out of the gate so it's not the best for solo, but once you get going you can handle a bit of everything. Speed up your draw with Campfire Tales, Valiant Sacrifice, Mustering the Rohirrim and Westfold Horse-breeders, plus the ever versatile Sneak Attack Gandalf. If you bring in Steward of Gondor from the sideboard it should go on Theoden, and you should mostly put Theodred's resource on Theoden is well. If there are no good targets in other players' decks for Unexpected Courage you can feel free to sub in the other two copies of Snowmane instead, since Theoden is the only one who really needs readying on your side, and the horse is cheaper and can be fetched by Horse-breeders.
You'll note the absence of Gamling - as good as the idea is in principle, I always find when I include him I spend too long trying to get set up with him able to recycle for me, at the expense of my early-game board-state, so I've always managed better without him. This may well be a case of me having played things wrong, but there it is. Feel free to try and slot him in if you like.
Played well against Treachery of Rhudaur paired with my brother's Gandalf deck - probably matches up well with decks that start well in general, but it doesn't take too long for the Rohirrim to get going. All in all, this is the most successful Rohan deck I've ever managed to put together, and I find it pretty fun as well.