Difference between varchar and nvarchar?

Storing Unicode Data

varchar: Variable-length, non-Unicode character data. varchar stores unicode data.
nvarchar: Variable-length Unicode character data. nvarchar stores unicode.

If you are using vchar datatype then each time you store data you first need the data to be converted into varchar then only you can store, this is not apply to nvarchar.

So if you are using nvarchar lot of your conversion task will be reduced. But nvarchar takes twice as much space as varchar, so before using this datatype considered this point.

With cheap memory nowadays I prefer nvarchar.
Post Reference: Vikram Aristocratic Elfin Share