Panasonic DMW MA-1 4/3 to Micro 4/3 adapter. Purchased used on eBay.
Pros: Electrical couplings for automatic aperture and autofocus. Good quality front and rear bayonets. Some of the more recent 4/3 lenses like the Olympus Zuiko Digital 50-200 mm f/2.8-3.5 SWD, mounted on a modern high-end body like the OM-1, E-M1 III and E-M1 II, autofocus well enough and fast enough to be usable for most applications.
Cons: Expensive. Plastic body may flex with heavy lenses. Autofocus with early and low-end Micro 4/3 cameras is essentially unusable with 4/3 lenses.
A newer version of this adapter is available. It is, as far as I can see, essentially identical to the first version except for small cosmetic changes.
A much cheaper no-name adapter from China, apparently a clone, is sold on eBay. Its exterior is black plastic, unlike the Panasonic model which is painted. It is largely built in the same way, except for a less careful blackening of the interior. In practical use, it seems to work just as well as the expensive Panasonic and Olympus models.
