Compare the negatives. The chances are the Argus' shutter is slow and it is overexposing. Overexposed color negative film will be more 'vivid'. Since you got it processed at the drugstore they may be expecting the typical overexposure that the average P&S or disposable produces and a properly exposed roll from the Nikon threw them for a loop.

Or it could be the other way round: the Argus is OK and the Nikon is (most likely) underexposing. I take it the Nikon's lens is free of fingerprints and fog...