Network Manager is the default manager for Ubuntu. This doesn't mean it's the best, but it does mean that it's a very good solution.
Depending upon your needs, Network Manager is most likely going to provide all the functionality that you need, however, I prefer to use wicd, as it interferes less with other configurations.
If you have reasons to leave Network Manager, I would suggest wicd.
Asking which program is 'best' is often not the best way to find what you need. If you have a specific problem with Network Manager ask about that specifically, instead.