Would switching the captain to damrod be better? Would Faramir better than king of men?

I'd say yes, and yes-ish. Damrod is perfect for leading Rangers, you gain a good shot, plus you can fit a couple more Rangers in with the points gained. Generally I'd prefer Faramir to a King, but in this case you don't really have the points to spend. Aragorn is soaking up most of it already, and he's a heavy load in 600 points. So rather than upgrading, you might consider downgrading, to a captain, Cirion, or even Beregond. The latter would give you at least half another infantry warband.