string
is an alias for global::System.String
. It’s simply syntactic sugar. The two are exactly interchangable in almost all cases, and there’ll be no difference in the compiled code.
Personally I use the aliases for variable names etc, but I use the CLR type names for names in APIs, for example:
public int ReadInt32() // Good, language-neutral
public int ReadInt() // Bad, assumes C# meaning of "int"
(Note that the return type isn’t really a name – it’s encoded as a type in the metadata, so there’s no confusion there.)
The only places I know of where one can be used and the other can’t (that I’m aware of) are:
nameof
prohibits the use of aliases- When specifying an enum base underlying type, only the aliases can be used