These are all made specificly  for predator calling. Lot of turkey hunters use the howlers as well. They are stacked and stretched differently than turkey calls.
Mark
Superpuppy
 Thin black top reed, thin natural latex bottom reed. Esy to run, higher pitched call. Great puppy yelps and whines.
Blackout 001 by 
Lonehowl, on Flickr
Dawn Patrol:
2 reed howler with a heavier yellow reed on top with heavy natural latex reed on bottom. Great all around coyote talker. mid pitched howls, barks and great ki yi's.

Challenger:
3 reed howler with yellow on top with 2 natural latex  reeds on bottom. Heavier, long range call.