Using 64 bit will make it easier if you'd ever want to migrate out to beefier hardware.
When architecture is different (for example 32bit vs. 64bit) you have to use pg_dump to migrate (or slony, or some other trigger-based replication).
When architecture is the same, you can migrate by stopping Pg, sending PGDATA directory to new machine, and then starting Pg there. Or using PostgreSQL streaming replication and failing over. Faster, cheaper, better.
If you know that you'll never move out of this VPS - you could consider 32 bit, but that's rather unlikely to assume.
depesz