It all depends on what outfits you plan on bringing. If it is more casual, then BJ. Like all the other ladies, keep it closed at all times and hang onto it tight around your arm. Sometimes they will just come by and snatch your purse when you're holding it lose and not paying attention. Or just take her out when you go out in the evenings to nicer restaurants.
All Parisians know about birkins so it will certainly catch someone's eyes, especially the bad ones. Better to be safe than sorry !