Micro Four Thirds: Which lens adapters are most compatible?

Using the micro four thirds (MFT) system allows you to pick from a wide variety of mount adapters which which to attach your old lenses (Nikon F, Canon EF, Pentax K, etc).

Question: Which common lens mount standards are most compatible with a MFT camera using an adapter? Are there some lens mount standards that give you access to the full functionality of the adapted lens on an MFT camera?