Need suggestions

I will create several databases on PostGreSQL. All the databases have the
same structure: same number of table/index.
I have two choices:
1. For each database, I create a new tablespace and create a new database in
the tablespace.
2. I only create one tablespace. Create all the databases on the same
tablespace.

What is the advantage and disadvantage of the two choices? For the first
choice, different database locates in different physical directory on the
hard drive. For the second choice, all the database locate in the same
physical directory.

Another possibility is to create a new "database cluster directory" for each
database. Then each database is managed by different database server
instance using different connection.

Which way is better? Thanks a lot.