Overall, routing is probably a better choice for most people, as it is more efficient and easier to set up (as far as the OpenVPN configuration itself) than bridging. Routing also provides a greater ability to selectively control access rights on a client-specific basis.
I would recommend using routing unless you need a specific feature which requires bridging, such as:
- the VPN needs to be able to handle non-IP protocols such as IPX,
- you are running applications over the VPN which rely on network broadcasts (such as LAN games), or
- you would like to allow browsing of Windows file shares across the VPN without setting up a Samba or WINS server.