Damian Widera-396333 (10/16/2009)
in terms of I/O we could assume fixed length data types are better than varying ones.
If, and only if,
a) the average length of data is only 2 characters or less below the maximum length. I'd never dream of storing address information in fixed length columns!
b) there is no need to preserve trailing spaces. If there is, varchar is the only option that won't corrupt your data.