Letter is the way to go for an initial introduction. As CW shown, some will even respond to them. It shows you made an effort and that you respect them enough to take the time in writing it. Even if no response to the letter, at least they have a name to go with your phone call.
I sent a few letters after drawing a tough leftover tag this year. I figure it demonstrates that you care enough to take the time to write something out and mail it, and also doesn't put a landowner on the spot like an actual call would. Haven't heard anything back yet but fingers are crossed big time