First, for a fitness bike I'd stay away from suspension front forks.
Second, can one really find a Specialized Vita Sport for around $500?
Thirdly, those Specialized, Giant and Marin bikes all have steel forks. A steel or carbon fork is not going to improve the ride of these aluminum frame bikes enough to satisfy most riders. Which suggests getting a steel frame bike.
Finally, if you can save up a little more or find one appropriately discounted, I'd also go with a Jamis Coda Sport Femme.