I built these decks to have a thematic experience through the Voice of Isengard, to use as many of the new player cards as I could, and to still be able to beat the quests. These decks handle the first and third scenario consistently well, and can beat the second scenario, but it is a lot more difficult (and the most difficult of the three, imho).

I wouldn't try these decks solo, but two-fisted they work together well and are a lot of fun.

Deck 1: Riders of the Mark

Heroes:
Eomer
Eowyn
Eleanor

Allies (25):
Arwen x2
Defender of Ramas x2
Eomund x2
Escort from Edoras x3
Gondorian Spearman x2
Minas Tirith Lampwright x2
Rider of the Mark x2
Westfold Horse Breaker x2
Westfold Horse Breeder x3
Westfold Outrider x3
West Road Traveller x2

Attachments (16):
Gondorian Shield x3
Horn of Gondor x1
Mighty Prowess x2
Rohan War Horse x2
Silver Lamp x2
Spare Cloak and Hood x2
Steed of the Mark x3
Unexpected Courage x1

Events (9):
Feint x2
Galadrihm's Greeting x2
Power of Orthanc x2
A Test of Will x2
The Wizard's Voice x1

Deck 2: Leaders of Men

Heroes:
Aragorn (Lore)
Imrahil
Theodred

Allies (27):
Envoy of Pelargir x3
Errand Rider x2
Faramir x1
Gandalf Core x3
Gleowine x2
Isengard Messneger x1
Orthanc Guard x3
Pelargir Ship Captain x1
Saurman x3
Snowborn Scout x3
Squire of the Citadel x3
Warden of Healing x2

Attachments (11):
Celebrain's Stone x1
Cram x2
Key of Orthanc x2
Steward of Gondor x2
Sword that was Broken x2
Ranger Spikes x2

Events (12):
Daeron's Ruins x2
Deep Knowledge x2
Legacy of Numenor x2
Sneak Attack x2
The Seeing Stone x2
Valiant Sacrifice x2

It's hard to give strategy advice without spoiling too much of the scenarios, but a few thoughts:

I built these decks with one core set. These decks were built with theme first in mind. There are lots of cards that would fit and make them powerful (Spirit Bofur, Eagles, Born Aloft, etc.) But I tried to stick to cards that made sense in a Gondor/Rohan/Isengard/Aragorn context.

One of the strengths of these decks is that there aren't essential cards. I've won games without SoG, without StwB, etc. The cards synergize well with each other, but don't need each other to function. Another strength is that they both excel at questing, because you want to finish the scenarios as fast as possible.

Almost every enemy is going to engage you right from the start, but that's part of the plan. Eleanor, Imrahil and Aragorn all serve as quality defenders, especially with the Gondorian Shield attached (Aragorn would have Steward on him to get the extra bonus). The Orthanc guards hold up surprisingly well against some of the weaker enemies, and were especially good in the first scenario. Otherwise, chump block! Eomer gets his bonus, Imrahil readies, and the fun ensues.

Timing up your Doomed cards is key. On some scenarios, it is better to play Legacy of Numernor and eat the 4 threat than it is to delay a turn (I've also done Legacy and Deep Knowledge for a 6 threat increase on turn one and it was probably the reason I won). Saruman, especially Sneak Attacking him after staging, is great, and more useful than Gandalf in most of these scenarios. His five attack is huge, and exiling the card can be clutch.

Finally, threating out was rarely ever a danger. One Galadrihm's Greeting typically took care of the Spirit/Tactics deck threat problems, and One Loragorn solved the Leadership/Lore deck problems.

If you're looking for a thematic experience in Voice of Isengard, try these decks out! They were lots of fun to play.