I've used both, but to be sure I understand correctly, what is the iron-on material you are considering? I made a family tree quilt and used the stuff you can print on through your printer and then iron it onto your fabric. It took forever to get it all ironed on. I then stitched around each image or leaf. The photos ran when it was washed in cold water. This was a long time ago and the product may have improved since then.
I've used Printed Treasures in several photo quilts and have been pleased with the results. One in particular has been washed several times in cool/cold water with very slight fading. All-in-all, Ive been happy with Printed Treasures. Just follow the directions on the package. The biggest problem I had with Printed Treasures was getting the peel-away paper off the back. I found that heating it slightly with the iron and then pulling the paper very slowly away from the fabric helped.
I'd love to see the quilt when it's finished.