1. nchar[(n)] (national character)

    i. Fixed-length Unicode string data.

    ii. n defines the string length and must be a value from 1 through 4,000.

    iii. The storage size is two times n bytes.

2. char [(n)] (character)

    i. Non-Unicode string data with fixed-length.

    ii. n defines the string length and must be a value from 1 through 8,000.

    iii. Storage size is n bytes.

 

3. varchar [(n | max)] (character varying)

    i. Variable-length, non-Unicode string data.

    ii. n defines the string length and can be a value from 1 through 8,000.

    iii. max indicates that the maximum storage size is 2^31-1 bytes (2 GB).

    iv. The storage size is the actual length of the data entered + 2 bytes.

4. nvarchar [(n | max)] (national character varying.)

    i. Variable-length Unicode string data.

    ii. n defines the string length and can be a value from 1 through 4,000.

    iii. max indicates that the maximum storage size is 2^31-1 bytes (2 GB).

    iv. The storage size, in bytes, is two times the actual length of data entered + 2 bytes

Reference:

https://docs.microsoft.com/en-us/sql/t-sql/data-types/nchar-and-nvarchar-transact-sql?view=sql-server-2017