Lvl 187. I can speak from experience that buck would be a good choice he is a solid operator. But so is caveria she is quite the game changer. You get an interrogating and everyone runs. But you have to play very patiently with her. Especially in ranked. When I play as her I'll usually hide until the last minute unless circumstances say otherwise. As long as you stay quiet you shouldn't have an issue sneaking up on people. From your list buck or caveria is your best options. Unless you still have vanilla operators you need?