There's basically 3 legendary scouts to choose from and personally I would use a scout over an auto rifle unless I'm working on an auto rifle bounty. I would try to get a medium impact/fire rate with decent perks because they are easy to use and there are a lot of different ones to choose from. The other archetypes shouldn't be overlooked but there are fewer types so fewer chances at getting a really good one. I'd start by checking vendor roles and gunsmith packages.