| I would probably err on the faster side, especially if you are something of a beginner as your user name indicates. That piece can sound really great slow, but it can also kind of die if not handled well. At the faster end of your range it has a little feeling of forward motion, while at the slower end it almost has an out-of-time feel. If you play really beautifully and expressively the slow tempo might work great, but you might risk putting the judges to sleep.
You might be interested to know that in the original opera, the piece is actually marked "larghetto" which is a little faster than largo. | 
