May I ask what camera and lens setup have you been using? If it's a zoom maybe you could search your image database for your most commonly used focal length. Then start with that.
Also ask yourself what subject out of those you mentioned you shoot the most of.
I've only been shooting a digital Leica M (M-E) for a year and a half and thought I was a 50mm shooter. I've found now I prefer the 35mm. The 35mm framelines almost fill the entire viewfinder which I now prefer.
I travel a lot and find the 35mm lens is all I need most of the time.
Your challenge once in the game is deciding the "look" you want your photography to say about you. Meaning what is your style.
Older non ASPH lens are going to render the classic look you may have seen from the Life Magazine years ago. Or the modern ASPH lenses are going to give that clinical look.
The rangefinder experience may completely change the way you think about photography.
It's a whole new experience from anything you may have already grown used to. It's like getting off the 6 lane expressway and touring the rolling 2 lane country road.
I would highly recommend reading Thorsten's M9 info here:
http://www.overgaard.dk/leica-M9-digita ... amera.html