Jaques,
The build quality of all Hasselblads is good. Nothing to worry about.
All throughout the "life" of the 500 C(/M) "micro-improvements" have been made to the internals of these cameras. Whenever a camera was brought in for service or repair, it may have been upgraded to include the then latest improvements.
Apart from that, being newer very likely means being less used, less worn.
So yes, buying the newest available will be a good idea.
But no, neither one will be better made or sturdier than the other.
The main differences between 500 C/M and 503 CX are:
- TTL-flash metering in the X
- Palpas antireflection coating in the 503 CX, providing better stray light reduction than the flat black paint used in the older cameras.
- The Acute Matte screen was "standard issue" in the 503 CX, while you have to buy one separately if you want one in a 500 C/M.
Apart from these, there is little to choose between the two cameras.
The "3" does indeed indicate the third generation, the marks of which are the last two things mentioned above.
The Acute Matte screen is very much brighter, but suffers from lower contrast compared to the older style screens. Overall, i'd say Acute Matte screens are to be preferred.
But i don't think the screen should be considered at all when deciding what body to get: they are freely interchangeable, and you can use any type screen in any type camera.
Both 500 C/M and 503 CX have the same vignetting mirror. You'll need a 503 CW or 501 CM to get a vignetting free viewfinder image.
