Which one sounds most exciting to you?
I did a sprint tri first, assuming I would walk the run portion (which I did) and putt-putt through the swim (which I did). My goal was just to finish, and I reached my goal. It was a tremendous feeling of accomplishment, and I proudly considered myself a successful triathlete.
Think about your goals, and what will give you the juiciest sense of accomplishment.
For example: do you like the idea of pushing yourself as fast as you can and going all out through every leg? Maybe consider the try-a-tri. Or do you like the idea of going long and pacing yourself with distance as your goal and speed as just icing on the cake? Maybe consider the sprint.
"If Americans want to live the American Dream, they should go to Denmark." - Richard Wilkinson