Welcome. Both are great cameras for very different reasons. Which one is right for you depends upon what you want to shot, how you want to print and how deep your pockets are.
The XPan is a wonderful panoramic camera with some very great lenses. While as Ben said, the lenses are somewhat slow, so existing darkness is a stretch. Not impossible, but you will be carrying a tripod. Everything you shoot with the XPan is a panoramic, horizontal or vertical, at the end of the day, a panoramic. While the camera is made by Fuji and they (IMHO) have a good reputation for well made cameras, long term, I am not sure how will be able to fix or find parts for the XPan. I think lenses at the wide and telephoto ranges are quite expensive. Again, do you need more than one lens all depends upon your style of shooting. I think it would be fun to force myself to think panoramic as a format, very creative but somewhat limiting from time to time. But perhaps that is part of the learning process.
IHMO, the S3 is a world class camera. Built in frame lines for 35/50/105, some of Nikons best lenses is a great place to start. I have an S2 and long for either an S3 or an SP. If I am every luck enough to get one, my kit would be a CV 15/4.5 (in F mount with an adapter for Nikon S mount), Nikkor 35/1.8 and a Nikkor 105/2.5. For my S2, I have a CV 25/4 (WORLD CLASS LENS, you can find a used one at
www.cameraquest.com for a very reasonable price, if you decided on the S3, jump on it, it’s a great lens), a Nikkor 50/1.4 Chrome Nikkor and a 105/2.5 Nikkor. I also have a 35/2.8 Russian and a 135/3.5 black Nikkor that do not get much use. CV lenses are great and if you can not find a very good Nikkor in your budget, I would say go CV. Not having a built in meter is a bit of a pain, but for some people, slowing down to think about what you are shooting is not a bad idea.
There are three reasons I use a Leica M6 as my main camera and not a Nikon SP or S3. First is lens selection. There is a much wider range of lenses available for the M mount at a wide range of both price and quality. Second is the lack of availability of a rapidwinder for the Nikon rangefinder. Rumor has it that Tom A has a few built, so if I had very deep pockets I think I could get one, but my pockets are being emptied for my family these days. IMHO, much more important. The third, and least important is the is the built in meter. While I am very comfortable with an external meter, I am lazy in my old age. I adjust my exposure as I am bringing the camera up to my eye and am pretty close most of the time so if I had to go without a built-in meter, I could. I did for several year with my M4-P and was quite happy.
I think the panoramic format costs more to process and print. This is something I think you need to consider as you make the decision. While film will be getting somewhat more expensive, are you able to process and print your panoramic film?
As you know by now, I would say go with the S3. If you can get the new 50mm Nikkor, it is one of the best 50/1.4 ever made by anyone.
Again, welcome, please keep asking questions and let us know what way you go. Also, if you do not pick the S3, please let me know where she is, I might take the plunge.
B2 (;->