In general it is best to move the data as a single object rather than serialize it member by member. As you say, the overhead of creating several byte streams to handle the various members outweighs the cost of moving a lot of data across one stream. Also, it is in general better to use the functionality provided by the
Java API rather than implementing your own (your code will be easier to write, read and maintain).
If you find you need to move a large number of these data objects, for listing purposes for instance, it is a common performance improvement to have two different objects. One with a few small fields for lists and another with the entire data set for editing.