In my experience it seems like many of the basic items are the same (hats, mugs, princess stuff, etc) I prefer the merchandise at Disneyland. It might just be the 50th items are still so fresh in my memory, but I have trouble picking what I want to buy at DL, but rarely buy things at WDW. Maybe DL's decision to hire Shag to do some of the designs has somthing to do with it
. I also found that the style of the shirts seem a bit more current.
If you'll be at DL soon, be sure to check out The Disney Gallery above POTC. They usually have quite a bit of merchandise that you can't find in any of the other stores.