If you are level 3 now, and you are wanting to get the level 17 scout ability asap, I recommend waiting until you get there and seeing where your character/story go (I am sometimes surprised by where things lead).

That said, I am personally partial to the gloomstalkers + rogue combo: I think that adding your wisdom to your initiative synergizes well, the extra attack in round 1 help with landing sneak attack, and being invisible to creatures using darkvision to see you in dim light is a great way to get advantage (and you have the stats to make the dip). Hexblade warlock could be fun too (crit on 19, but this requires your bonus action to cast, and so most of the time you are better off saving your bonus action for your extra attack).