As with anything there are a variety of collar/lead combos used in the show ring. In the toy rings you will usually see rescos or what I've always been told are "kind collars", these collars have a wider chin/neck support to prevent tension on the trachea. Here are a couple of links
selection of collars -
Show Leads & Collars | PetEdge.com
kind collar -
The 3c's Dog Show and Grooming Supplies
Teresa