* lár (laar): This is the most common and generally applicable word, meaning "middle" or "center." It's suitable for geographical centers or the center of something.
* ionad (ionad): This translates to "place," "center," or "location." It's often used for a central point of activity or a central institution (like a community center).
* croí (cree): This means "heart," but can be used figuratively to mean the "center" or "core" of something.
Therefore, depending on what you mean by "center," lár is usually the best choice, but ionad or croí might be more appropriate in certain contexts.