I had a similar dilemma myself recently:
1. I now own a Fuji X100s and LOVE it for street photography. Please note, I'm a little biased here because it is my newest toy.
2. I considered it, but the 5DIII is still huge and draws a lot more attention in comparison to the X100s and. (I've shot a fair bit of street photography with 5D III + 50L combo).
3. I still do want to rent a Leica myself and try it out. However, with the auto-focusing being so darn good on the two aforementioned cameras, I find myself wondering how many shots I would be willing to miss to obtain the "Leica experience." All comments mentioned below about Leica assume a Leica m9 with Leica class.
One thing to take into consideration is what "type" of street photography shooter you are. If you hang back and wait for shots, you are less likely to be noticed with any camera. Mark Carey does some amazing street photography work with the 5DIII. However, if you are a "wanderer" like me, I have found the X100s to be a dream in good light (phase detect focusing engages in good light). I'm sure the Leica would be just as great.
Each setup has it's own pros/cons. I'll give my view of each. For reference, I have owned the following:
Currently owned: Cameras - Canon 5D3, Fuji X100s.
Lens - Canons: 50L, 85L II, 70-200 IS II, Tamron 24-70,
Previously owned: Cameras - Sony RX100, Sony NEX-6, Fuji X100, Canon T3i,
Lens - Canons: 35L, 40mm pancake, 50 1.8, 85 1.8, 18-55 IS II, 70-200 f/4L,
Sigmas: 30 1.4, 50 1.4, 85 1.4, 17-50 OS, Tokina 11-16
Auto-Focus:The 5D III + Sigma 35 wins. Fuji X100s is no slouch in good daylight, but it's still no 5D III either. In the dark it is still accurate, just slower. However, I find it good enough about 95% of the time. Leica - no AF
Manual focusing:Winner: Leica - Duh. In second place comes the Fuji X100s. The focus peaking is great and digital split focus is pretty cool. (I prefer the focus peaking). The Fuji also has a distance meter that is a GREAT help if you want to use zone focusing. I hate manually focusing the 5D III. With world class AF, why would I anyways?
Size:Fuji X100s wins here - the smallest and only "pocketable" option of the three. I love the small discreet size. This also plays into the "stealth" factor as well. Leica's are also great, just not quite as small. The 5D III is a huge beast. Gaffer taped or not, the 5DIII is really noticeable.
Lens options:5DIII and Leica tie. However, if you are comfortable shooting 35mm only, then the Fuji lens is actually really good.
IQ:5DIII ^ Leica > Fuji. It's about what you'd expect. The 5DIII excellent sensor + Sigma 35 will offer the greatest resolution photos. Though, IQ isn't all about resolution and some will argue and say the Leica has that special "Leica" look that trumps all. Though not quite as good as the other two, some people love the way that the X100s renders color. Even with the lowest resolution of the 3, the Fuji's 16mp sensor still leaves room for decent cropping. I have no hesitation in using the Fuji for professional work and have used it multiple times for that use.
Handling:Many will say the Leica. I've never used one, so can't comment. However, I can say the X100s is the most fun to use and is my favorite camera EVER. The manual dials are great! Also, see the "viewfinder" section below) I love my 5DIII and it feels great for a DSLR; but... it's not very fun to carry around and use for a long session.
Viewfinder:Fuji X100s BY FAR. The hybrid viewfinder in the X100s is the best I have ever used (many reviewers state this as well). I won't even attempt to explain it. Just about every review gushes on about how great it is. I'd recommend trying one for yourself. The Leica's are great if you want the rangefinder experience but lack any "live view" options. The 5DIII is good and but "live view" is only available via the LCD.
ISO performance:Fuji X100s will offer the cleanest files at low light, even beating out the 5DIII. This is about the only place that Leica comes in last.
Build:All 3 have excellent build quality so no reasons for concern here. (please keep in mind that the Sigma 35 and the X100s are NOT weather sealed)
Discreetness:Fuji X100s. It is the smallest and quietest camera of the 3. The shutter is hardly perceptible in most environments, even for the photographer. I've heard the Leica shutter is pretty quiet and as mentioned earlier, it's smaller size. That Leica logo may attract attention from lustful photographers here and there. The 5DIII's silent shutter is great, but it's a huge beast.
Overall:That's up to you. I went with a Fuji X100s for street shooting and it comes with me as my every day camera as well. I keep my 5DIII at home for portrait and event shoots. For me, it was an "either/or" situation, meaning I can't afford a Leica without selling my 5DIII kit. No matter how great the Leica's manual focusing is, there are just times then the 5DIII's auto-focus does what I simply couldn't using manual focus (*note my limitation, not Leica's). If Leica ever makes an AF-capable body, I'll seriously consider selling my kit for it. My current setup works perfectly for my needs; Fuji X100s + Canon 5DIII, Canon 50L, Canon 85L II, Tamron 24-70 VC, Canon 70-200 IS II.
*Side note #1: Please note that I have never owned or used a Leica. My knowledge of them is limited to the 40 or 50 hours I spent researching them when I was seriously considering buying one. I think they are amazing cameras, but it just isn't a good fit for me currently. If money were no issue? You can bet I'd have one.
*Side note #2: If you decide to go with the Fuji X100s, buy two extra batteries (as the battery life is about 300 shots) Also, be sure to buy a high-performance SD card for the X100s as it improves the cameras performance noticeably. Another bonus is the 1/4000 flash sync speed. I haven't used this yet, but it can allow for some amazing creative opportunities with an external flash.
And... first post done.
