I was headed for my first elk hunt in '96 and pondered the same issue. I got the Woodwise Hyper Hot Cow Call, and had the experience of a lifetime on day three of the hunt.
The Woodswise call is a simple barrel reed call that is easy to master. The tape is excellent. The main guy in the video, Jerry Peterson, takes you through all the various calls. It also comes with a cassette tape you can play in the truck... Jerry also demos how to use a combo reed and bugle tube.
I was still a bit skeptical of how "aggressively" the bull seemed to react to the call in the video. Well, it was not an exaggeration! My partner and I were working our way down into a basin of heavy dark timber using our cow calls to talk to one another and stay parallel. A five point roared at us from inside a 100 yards. Luckily we had just broken out into some aspen with decent shooting lanes. The rack is on my wall. It happened just like the video depicted. The next year everyone in camp had the Woodswise call and one guy was almost run down by a bull after using it.
There are several varieties that all work. I just happen to have personal experience with the Woodswise call. Their website is
www.woodswise.com The gent pictured on the home page is Jerry Peterson, their “callmaster.”
Good Luck!