"Interoperability" means that we would prefer it if SSL clients can actually connect to our server; otherwise, having a SSL server would be rather pointless. In practice, average clients only support two curves, the ones which are designated in so-called NSA Suite B: these are NIST curves P-256 and P-384 (in OpenSSL, they are designated as, respectively, "prime256v1" and "secp384r1").
If we use any other curve, then some widespread Web browsers will be unable to talk to our server. Use P-256 to minimize trouble.