The Big Con Approach is not only super efficient (given the perilous nature of GTA Online), but it's also quite fun. It allows the player to infiltrate the casino in disguise. This approach, too, helps the player avoid unwanted attention and keep a low profile, which is always helpful in GTA Online.
Aggressive is good for newer players however it does end up in a lot of money loss. After you've got the gist of it, alternate to doing Silent and Sneaky in place of aggressive for a bigger payout. After you've selected your approach, you'll need to select your support crew before you can do any of the prep missions.