Hi,
As a general rule, the faster the shutterspeed, the better the sunball and rays. On film, you need to shoot ~1/120th to start seeing sun rays. With digital, perhaps faster.
The higher the dynamic range of the camera, the better the sunball you can get.
If you expose the scene for the sunball by stopping down and using a fast shutter speed, then you will get an overall dark photo. Cameras with higher dynamic range will be able to lighten up that dark area and show detail in the shadows better.
Either way, an exposure is an exposure though - in the example above, it's what you do with it afterwards (in postprocessing) that matters.
Cameras that can flash sync faster than 1/250th are a good start.
Some cameras that have good DR and fast sync are: Canon 1DmkII, 1DsmkII, Fuji S3, and perhaps the Canon 20D and Nikon D70 and Nikon D2x.
HTH
James