It's a tough decision.
It seems to me that a Nikon RF user/collector is eventually going to wind up with an SP, so the main question is when and how.
I bought my cameras in order of price ... a Kiev 2a, then an S2, then an S3, then an SP. The S3 and SP are identical except for the finder. Also, their controls and handling are identical to a Nikon F, minus the mirror box (and the SP and S3 are a little smaller).
For what it's worth, I tend to use both cameras equally. I'm currently favoring the S3, but I go through cycles. When I was doing newspaper work, I carried both.
The SP wide-angle minifinder is really easy for eyeglass wearers to see the 35mm and 28mm frames, but I do sometimes get disenchanted with the smallish view. The S3 is wonderful for 35mm lenses ... though a bit hard for eyeglass wearers to see the whole frame ... I tend to concentrate on the corner of the picture where framing is most critical. For those who don't wear glasses, the S3 finder can be very capable of shooting 28mm lenses. Its full coverage actually seems pretty close to 25mm. With the S3 finder, you can easily see the difference between th4e 35mm and 50mm lens frame, and the 28mm is about that same distance beyond the 35mm frame. You can also see, using the parallax etchings, that parallax isn't a hiuge factor with really wide lenses, especially since the Nikon S mount only focuses to 3 feet (probably that's the system's biggest shortcoming). In general, the SP is best for 28mm lenses and the 85 and 135mm lenses. The S3 is of course optimized for 35-50-105mm, and that's a dynamite group of rangefinder lenses. Throw in a 21mm or 25mm CV and you're in business for the rest of your life.
I'm not acquiring cameras these days, but the S3-2000 is awfully tempting. I think, adjusted for inflation, that must be quite a bit less than these cameras cost in the 1950s and early 60s.
And Brian is right about the new version of the 5cm 1.4 lens. That's a super-rare version that's probably worth half the cost of the camera itself. I assume it's got a formula very close to the SLR 50mm/1.4 of the 1960s, and that is an extraordinary lens. It keeps the contrast, tones and sharpness of the original RF version, reduces the wide-open vignetting while increasing wide-open contrast and makes the background out-of-focus areas much, much smoother. I'm attaching a portrait of two Bosnian war survivors I took in 1996 with a 1960s-vintage Nikkor SLR 1.4 on an early digital camera, the NC2000, shot wide open and with the digital crop factor giving it a 75mm field of view. It's one of the best lenses I've ever shot with.
