Passive magnetic gravity compensation may be a very feasible alternative to commonly used mechanical or pneumatic solutions for vibration isolation systems. This paper discusses a study on the optimal design of an ironless magnetic spring with a horizontal airgap for use in an electromagnetic vibration isolator. For such systems it is often preferred to combine a high force level with very low spring stiffness in order to achieve a low resonance frequency. Two optimization methods are used to achieve these properties and their results are compared. This study aims to provide more insight in the limits of the proposed topology on the achievable vibration isolation performance of permanent-magnet based springs as well as the feasibility of the modeling and optimization tools.