Returning 'IList' vs 'ICollection' vs 'Collection'

Question

I am confused about which collection type that I should return from my public API methods and properties.

The collections that I have in mind are IList,

Answer 1

ICollection is an interface that exposes collection semantics such as Add(), Remove(), and Count.

Collection is a concrete implementation of the ICollection interface.

IList is essentially an ICollection with random order-based access.

In this case you should decide whether or not your results require list semantics such as order based indexing (then use IList) or whether you just need to return an unordered "bag" of results (then use ICollection).