[Keeper of Dol Guldur]

Well, I too pictured them as big fluffy wolves on 'roids, twice the size of a real wolf, but not as big as a bear ... with pointy snouts and jagged craws.

But the hyena idea is not an innaccurate depiction. The definition of wolf in a dictionary often makes mention of "other similar species; hyenas".

Of course, that simply means when I read the books, I have a different idea in mind than what I've seen in the movies.

It seemed to me that Saruman was the only one employing warg-riders ... who were smaller orcs of the Misty Mountain variety (obviously a warg would have trouble supporting a massive Uruk-Hai) ... goblins of the like from the Hobbit.

But there was mention of wargs howling on the Pelennor, and fearful cries, weren't there? And Gandalf did mention that Sauron housed wargs (and werewolves - his loyal creatures, remnants of his force on Tol Sirion) at Barad-Dur.

Naturally harsh, barren terrain like Mordor wasn't prime wolf territory like the pine woods around the Misty Mountains ... so that would be a big explanation.

As for the best way to combat wargs ...

Arrows. Archers on the high ground have always been effective against cavalry.