I've seldom found shutter priority to be that useful, except when a very specific shutter speed is absolutely critical, such as when shooting panning shots, or helicopters, or when a very fast minimum speed is needed and there is plenty of light, such as when shooting from a fishing boat in the summer under bright ocean conditions, and 1/500 to 1/800 is really very helpful, and there is again, a LOT of light.
For the beginning people photographer shooting in natural light (not flash), I think using AUTO ISO in Manual mode is a good method, especially for Nikon or Pentax shooters, whose cameras offer this feature in a well implemented manner. Basically, it's a Manual exposure mode, where the photographer selects the best shutter speed and f/stop for the conditions. Then, the camera can raise or lower the ISO value as needed, to make that f/stop and that shutter speed deliver the proper exposure. This frees the photographer from constantly needing to adjust three different values, and allows the photographer to focus on the subject, and on composing the photos, and waiting for the right timing to snap them.
Using Nikon's matrix metering, and an exposure of something like f/5.6 at 1/500 second, it becomes a trivial matter to shoot a portrait session at the beach with a 70-300 zoom lens, or whatever, and not have to constantly adjust,adjust,adjust. Shoot a shot, look at the LCD and histogram....if it needs more light, click in a little Plus Exposure Compensation to the camera....BOOM!
I really like f/5.6, f/6.3, and f/7.1 for portraiture. I do not favor wider f/stops like f/2.8 or f/3.2 very often, unless it is just one, single individual. When there are two people in a photo, stopping the lens down to f/5.6 or f/6.3 or f/7.1 is my normal starting point.