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the answer for your question is One we can't answer.
We only can tell you the difference and you must decide then what you need/don't need.
char indeed reserves the spaces (1byte / Char)
varchar doesn't reserve the space but will use dynamicaly (1byte / Char)
the nChar and nVarchar are the MultiCode page versions of the 2 above.
For this expansion they indeed need 2 bytes for each char
So Now you need to decide do you need multiCode text to be saved in the database?
Yes : Use the N-Versions
No : Use the normal versions
regards
poor beggar