I have a list of Customers. Each customer has an address and some customers may actually have the same address. My ultimate goal is to group customers based on their address. I figure I could either put the customers in some sort of list-based structure and sort on the addresses, or I could drop the objects into some sort of map that allows multiple values per key.

I will now make a pretty picture:

List:
A1 - C1, A1 - C2, A2 - C3, A3 - C4, A3 - C5

Map:
A1 A2 A3
C1 C3 C4
C2    C5

Which option (or any others) do you see as the best solution? Are there any existing classes that will make development easier?