Actually no snake is 'aggressive' except black mambas. Snakes are defensive if they think you are going to hurt them.
And I would put Caesar my SD retic up against any snake for mellowness. Caesar has never bit me and the only time he has been pissed off is when I tried using a hook to touch him on the head. He opened his mouth and hissed at it. Since then I quit and just use a twisted up paper towel which he is fine with for when he thinks its dinner time and gets excited. Otherwise I can just reach in, scoop him up and he will sit on me or stretch out on the bed or couch and relax or explore.