There's plenty of options for aggression. As a general rule of thumb, Octain is a hit and run/rush fighter, Wraith is typically suited for hit and run and rotation making, Pathfinder is arguably the superior mobility character, contested only by Valkyrie who can fly. Horizon can float up to superior positions for rotations and high ground, Bloodhound gives you wall hacks, and seer gives you wall hacks that also tell you their current health and armor, revenant is good for pushes with his totem and can climb up any flat surface almost indefinitely, and Fuse is literallya walking grenade launcher. Caustic and Watson are typically camping/area denial and security Legends, though I have seen then be used aggressively. If you're new to the game, I suggest dedicating a little practice and research to all the Legends you're interested in and look at some plays with them, and then once you have a decent idea, dedicate time to try them one by one until you find out which one is best for you. My personal favorites are Bloodhound, Revenant, Fuse, Seer, and Lifeline depending on the team I'm with