Is it just that nvarchar
supports multibyte characters? If that is the case, is there really any point, other than storage concerns, to using varchars
varchar: Variable-length, non-Unicode character data. The database collation determines which code page the data is stored using.
nvarchar: Variable-length Unicode character data. Dependent on the database collation for comparisons.
Armed with this knowledge, use whichever one matches your input data (ASCII v. Unicode).