Costco vs. Sam's Club?

So, we used to have a Sam's Club membership.  While I loved it, we let it expire at the end of 2010 because I found I didn't go there as often as I would like.  Plus, I used it mainly to purchase supplies for my business (making wedding and special occasion cakes), and with expecting baby #3 I decided at that point to stop taking any additional orders until 2012.

There is a Costco just down the street from the local Sam's Club.  I've only ever been in Costco twice.  I didn't see much of a difference, but I had kiddos with me both times I went, so I couldn't really compare things.  Anyone had any experience with both of these stores?  Do you think it's worth it to have a membership?  Any tips or tricks to getting good deals at either of these places?  I would probably purchase mostly bulk baking supplies plus some fresh fruits, veggies, etc...