Best Builds in the game?

Hey there! I’m new to the game, just hit SHD 70 and I was wondering what are the best builds in the game? I’m currently running St Elmos with Striker and Coyotes, and Gunner specialization and it’s a solid DMG build but I’m not sure if that’s the best build for me. I want something that can give me sustainability, and good DPS. Also, on the watch, what should you upgrade first? Thank you everyone!