First - do you have a specific problem? The time to dump an image to the memory card varies a lot from camera to camera and the best solution for your problem is probably to try to investigate it yourself.

Also why are you focusing on the time it takes dump the file to the memory card? With the often large buffers of modern cameras you can often continue to take images while the camera processes and saves previously taken ones. The total time required to get the image written to the card is rarely a relevant measure.

To answer your question:

As a general rule the saving of a JPEG is probably a lot faster. Sure RAW files are less processed and can begin to get dumped to the memory card almost instantly but digital cameras that are set to render JPEG with the standard settings usually employ ASIC circuitry for the job. These have vastly better performance than general processors in terms of speed. Fancy picture styles that are not supported by the ASIC processors can therefore take a lot of time to process.

Note that when you increase speed of the memory card and controller (while retaining the same file size) the time to save the image to the memory card decreases to the RAW file's advantage. Imagine for example an infinitely fast transfer speed - an unprocessed file would take no time to get saved while the processed file still has to be processed. This may be a reality if the raw output file size settles in the future and that happens long before the maximum transfer speed possible is reached. I highly doubt that it will though since very few people require the instant dump to memory card feature.