This really depends on what routes you want to fly.
If you want the 6-7 hour flights, then the 767 will do well. But if you want the flexibility to fly 12-14hour flights aswell with one fleet type, 787 is better option. The 767 has a limited range but depending on your hub this might not be an issue. For example, 767 can not make a good SIN to europe hop. 787 will do better. But if your hub is jfk, well then a 767 will fly everywhere that you need. A300-600 makes excellent money aswell.