Both are very nice to visit.
At St. Augustine you will a larger selection of species. I have had good and bad experiences there.

Gatorland does not have the selection of St. Aug but I have always been treated very well and they have pretty equal amounts of shows. Gatorland has a more entertainging type show format where as St. Aug seems more educationally based.

Where you are staying will play a role as well. We usually stay in St. Augustine for a couple of days and hit the Farm while there. But to go to Gatorland from St. Augustine is a couple hour drive. Vice versa on staying in Orlando and driving to St Aug.

I think you will have a great time not matter which you attend.
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2 A. Miss at 8'
5 A. Miss at 3'-5'
1 C. Nil at 9'
1 C. Croc at 6.5'
and
6 A. Miss/C. Croc 2'-3'