American Alligator. Partly because they're relatively cheap, interesting ones are usually available on the market, and it's an easy early habitat that I can make look decent without spending a lot (no hard shelter requirement). The other reason is because I've always enjoyed seeing the alligators around the central Florida waterways. (It bothers me that there's no tropical zoo zone in Florida in the game because I have to either have a Florida zoo that gets a lot of snow or a tropical "Florida Zoo" no where near Florida.)