In the event that the chief governing body, city council or board of park commissioners of such city shall exercise such right by condemnation such body may do so under any laws provided for the condemnation of real property or eminent domain or under any provision of the charter of such city granting to such body the right of condemnation or power of eminent domain; or, it being for the best interests of such city, such chief governing board, city council, or board of park commissioners shall have the power and authority to acquire the rights by purchase, taking into consideration the present worth of such right to exemption and the probability or improbability that such exemptions would ever be used as an offset to future assessments for benefits.