You're mixing apples and oranges (i.e. "M" and "R" Leica models)....
Originally Posted by melmoth
Leica "R" models are SLR cameras, and suffer from the same shortcomings as other SLRs - mirror slap, vibration, etc...
Small, manual, precise - get any "M" model that fits you. However, before taking the plunge and spending all that cash, you'd better test drive it, or first get some experience with another, cheaper, RF camera, just to see if this whole "RF" thing is for you.
I have several Leicas, and find I like my M2 the most. Having the meter in the M6 just distracts me. With all-mechanical meterless body (i.e. M2 or M3), I first meter the light, and then shoot without distractions, concentrating on the scene and the framelines.
Silent, quick, and reliable....
However, Leicas (and other RF cameras) have their limitations - the closest focusing distance with a 50mm lens is usually 0,9 meters or thereabouts. There's also the parallax problem, which is not always obvious.
In short, you can't (and won't) get a definitive answer from anyone else but yourself. The choice depends on your shooting style, kind of shots that you take, etc.
But, I'd agree that for dimly lit spaces without flash, a rangefinder is the way to go, particularly if you don't want to stick out or be noticed (or heard).
After shooting 35mm format for a year almost exclusively with a Leica, I shot a roll with my old Nikon FM a few days ago. It felt (and sounded) like a Colt 45 compared to a Leica Big, heavy, unwieldy, and loud. And the mirror slap (and the vibration) is awful! I wondered how I ever got a sharp negative with it!
OTOH, if you want to get really close (e.g. 0,5 meters or so), SLR is the way to go.
For quasi-silent SLR shooting, I find my Nikon N80 much better in that respect - it's the absolute winner in my SLR collection, as far as "silent shooting" goes. But, Leica glass is the all-round winner as far as final quality of the shot is concerned.
In short, you should first re-examine your needs carefully. If you do decide for a Leica, take some time to get familiar with different models, viewfinder magnifications, etc. There are many good resources on the Net available.
Let me reiterate - you could (and probably should) get a cheaper rangefinder first to "test the waters". Yashica Electros come to mind. Yashica Lynx 14e also has excellent lens (45/1.4), although it's a bit on the large side.