nvarchar(max) vs NText
The advantages are that you can use functions like LEN and LEFT on nvarchar(max) and you cannot do that against ntext and text. It is also easier to work with nvarchar(max) than text where you had to use WRITETEXT and UPDATETEXT.
Also, text, ntext, etc., are being deprecated (http://msdn.microsoft.com/en-us/library/ms187993.aspx)
ntext will always store its data in a separate database page, while nvarchar(max) will try to store the data within the database record itself.
So nvarchar(max) is somewhat faster (if you have text that is smaller as 8 kB). I also noticed that the database size will grow slightly slower, this is also good.
Go nvarchar(max).
VARCHAR(MAX) is big enough to accommodate TEXT field. TEXT, NTEXT and IMAGE data types of SQL Server 2000 will be deprecated in future version of SQL Server, SQL Server 2005 provides backward compatibility to data types but it is recommended to use new data types which are VARCHAR(MAX), NVARCHAR(MAX) and VARBINARY(MAX).