Trek is hard to beat. Frontiers is another good one.

However, if its perdiz you wish; you may find it better in Uruguay. It is the world's best, IMHO. There are simply more birds there. Season is limited, so be sure you are booked at the correct time. Duck shooting is similar in both places.

Stay at one of the old estancias if at all possible, much more fun and all are historically significant of themselves.