ESI Corporation is the best mediclaim service provider for those who are under the ESI scheme. For those out of coverage of ESI, you can select from the immense of offers that you get from the service providers. But if the policy can be linked to Employees Compensation Act it would be good.
Additional advice not forming part of the answer to the question: Mediclaim is not an employee benefit as per statute. But once introduced, you may not withdraw it because by then it would have become part of service conditions. Being a start up establishment, therefore, think of it twice before introducing it.