If you're referring to the OM system used in Olympus cameras, the best memory card would depend on the specific camera model you have and your intended usage.
In general, it's recommended to use SD (Secure Digital) cards with a UHS-I or UHS-II speed class rating for Olympus cameras. These types of cards offer faster read and write speeds, which can be especially beneficial for capturing high-quality photos or videos, or for continuous shooting.
Some popular brands for memory cards include SanDisk, Lexar, and Kingston. It's important to choose a reputable brand and ensure that the card you select is compatible with your camera model.
In addition to the speed class rating, you may also want to consider the storage capacity of the card. The amount of storage you need will depend on how frequently you use your camera and how often you transfer files to a computer or other device.
Overall, the best memory card for your OM system will depend on your specific needs and preferences. Be sure to do your research and choose a high-quality card that is compatible with your camera.