I sometimes forget which is which. I now remember this as folows:

• First, these work on based spaces so we always need to think of based points.
• Wedge is a sum, so it's going to be some type of union. It needs to identify things, so it better be $A \cup B / \sim$ where $\sim$ identifies based points.
• Smash is a product, so it's going to be some type of product. It needs to identify things, so it better be $A \times B / \sim$, where $\sim$ crushes together anything that has a based point. So $(*, a), (a, *), (*, *)$ are all crushed.
• If we don't remember the "sum" and "product" bit, and only remember "wedge" and "smash", then "wedge" starts with a "w" which looks like \/so it should be a union.