I'd definitely be a conniving manipulating tribal leader. Tricking neighbors into giving me concessions until I'm so powerful the rest will simply fall in line
I have no idea what kind of leader I'll be but I can tell you one thing, I want to be a Viking and run around hitting people with my axe, just like the Norse gods intended
I would probably have to go with a combination of the two. There is a time for diplomacy after the viking presence has been accepted but first you would need to use force as you make your way inland.
As cool as being a badass conqueror would be, I'd probably try to be more diplomatic. "Stay your blade from the flesh of the innocent", as the Creed mandates!