If you like the rangefinder system, you simply can't go wrong with a Leica M body. The M8 is a pretty decent camera, albeit with a slow and crappy screen... and a poor sensor in terms of color tonality and ISO performance for the money. As with the M9 (which I owned for a while), the images are excellent only after some tweaking in Photoshop but the Leica glass does give you a different look to your images. The rangefinder way of shooting (focusing and framing) also takes some time before you get used to it, so be patient if you end up getting one. Personally I'll stick to a film M body anytime for the full rangefinder experience.
The NEX system is small and great (I have the NEX-5n) but the handling and feel doesn't even come remotely close to a rangefinder way of shooting and ends up feeling rather gimmicky. I don't know much about the Fuji X-Pro1 system but I reckon it probably is a cracking camera in many ways. I've tried it in a local shop and it's a very nice camera indeed. At the end of the day, all this depends on your needs and wants. The M8 = manual focus rangefinder, XPro1 = quick autofocus camera, NEX = capable small camera.