You've mangled the link to your gallery - correct link is here
I wouldn't submit any of the individual images you picked out for an application. I can't make any comments on technical quality from such small sizes (we'd need to see the original image), but there aren't any standouts, IMO.
What combination of 3 was rejected before? You'll want to have 3 different types of shot (a portrait, a studio still life and a landscape, for example). Stay away from flowers, sunsets, puppies and kittens unless you have something exceptional. Your gallery has mostly travel images, and some could use a little post processing to make them more "stock-y". Perhaps you could find a friend to model for you to add a different type of image to your application set?
Don't sharpen and be sure to check the image at 100% for sharp focus, absence of noise and artifacts. You can use the iStock critique forum (you'd need to buy credits to be able to post) for additional help.