Ugh, I just went through this. The bottom line is that it's impossible to find effective blackout curtains in white/cream that aren't made of yucky plastic-like materials. It seems that the materials that generally make for a good curtain are mutually exclusive of the materials that are good at blocking light. Of course, darker fabric will block more than lighter fabric, so if you were looking for a darker color curtain you might be able to find a reasonable compromise. I was unable to find a reasonable comprise in white/cream after buying dozens of panels from all the stores you mentioned.
I ultimately decided to go with two layers: a layer facing the room made of the materials I liked in the color I liked, plus a simple low-profile vinyl roll-up shade mounted in the window frame. It's not ideal, but it was the best I could find after 2 months of looking.
Interestingly, I found that JC Penny has a very good selection of curtains! (I was referred there by a friend; I never would have imagined it.) The panels I wound up with are Royal Velvet "Grandeur" in ivory. They are significantly nicer than anything I found anywhere else.
Here's the link: http://www.jcpenney.com/dotcom//for-the-home/departments/window-treatments/categories/curtains-drapes-/royal-velvet-grandeur-silk-back-tabrod-pocket-curtain-panel/prod.jump?ppId=pp5001120010&catId=cat100490004&subcatId=cat100260213&deptId=dept20000011&N=1639&Ns=PLH&Nao=72&pN=4&topDim=Brand&topDimvalue=royal+velvet&dimCombo=Brand|&dimComboVal=royal+velvet|¤tDim=Brand¤tDimVal=royal+velvet