GC Filing - birth certificate?

Hi,

If original birth certificate is not available, then what is the best alternate to submit while filing for GC? The options provided do include an 2 affidavits by people alive at the time of birth, a certificate of non availability or incomplete birth certificate. But which of these alternatives would be the simplest ( in terms of additional supporting documentation) and prove to be the strongest for the case?

Thanks,

Anita