Rent a leica, that's a wonderfull idea... Well, I got a R3 but many people says that it's more a minolta camera that a leica, ando old piece tecnology. But one can get at a decente price. For what i have read around the net, the best mechanical leica slr, it's the SL2.
The leicaflex has the support everything fame, build like a tank. I went to the r3 since i wanted one with AP. R4 and 5, several people point out that they are extremely loud and the r6/6.2 are in the top preferences since it's the return of the mechanical slr.
I like my r3, it's simple, no programs and i have manual or auto. Of course, if bateries fail, no taking pictures...