I prefer an RF, now that I have one. I never really shot with 35mm SLRs, only MF, but here is why I did not like using the Pentax 645NII for anything except portraits :
1. Heavy
2. Bulky
3. Loud
4. Could not trust the AF to be really where I wanted it.
5. Too easy to shoot through frames without thinking.
6. Shake - the clarity of my RF stuff is obvious compared with that of the MF SLRs I've used.
What I liked about the SLRs:
1. For shooting portraits - an SLR (with AF) is the best for business
2. FAST lenses - like the F2 on the Contax, the 1.9 on the Mamiya 645, and the 2.8 on the Hassy. Of course, with 35mm RFs, you have even fast lenses.
3. Shooting 35mm SLRs - they are FAST. Fast AF, fast shutterspeeds, fast film advance, etc.
4. Lots and lots of accessories - of course Leicas have lots too. But the Nikon F series is impressive.
5. Durability of the camera in hard times. Go ahead and drop your Nikon F. Now drop the M7. Which will you shoot the priceless moment with?
What I like about my RF cameras :
1. Light weight
2. Small
3. Sharp optics (made more obvious by mirror-less operation)
4. quiet (makes a BIG difference in street photography as you know)
5. Forces me to really think more about my shots (versus AF SLRs)
6. I find the RF focusing to be sharper than SLR focusing.
7. Less expensive to use (fewer, better shots means less money spent on crud).
8. Better lenses . . . . maybe - like the Mamiya 7 series, and the Bronica RF645 - better than the MF SLRs.
9. You can bring a small tripod because the camera DOESN'T weigh a million pounds. This is a big one for hiking. I hate dragging my huge Manfrotto around - it looks too pro.
10. Less battery consumption - if you don't like buying batteries all the time.
11. If you bring the Leica or Zeiss RF, you have the best lenses on the planet. Period. No 35mm SLR will give you better results.
12. You can melt more into the nature you are photographing because everything about the rangefinder is low key unlike the shocking presence of something like the F5.
I have shot in ALL formats, used every brand except Contax, and will say that I would bring the RF645 on a trip to . . .anywhere . . . before any other camera I've used. Except if I were to shoot portraits, in which case the Pentax 645NII would be my friend.