Answer:
This is truly going to be a matter of personal preference and fit. Generally speaking, however, most clay shotguns have longer barrels and interchangable chokes, and often a Monte Carlo style stock. If this is something exploratory, consider the following lower-priced guns:
CZ Canvas back 12g 28", Charles Daly 206 12g 30"
If this is something you want to take more seriously, look into something like a Browning Citori or Winchester 101. Happy shooting!