The OP_COMPRESSED spec states

When compressing, clients MUST use the first compressor in the client's configured compressors list that is also in the servers list.

But the compressor to use is retrieved from the server description which is set directly from the isMaster reply. So we always take preference of whatever order the compressors are in the server reply.

In practice, this may not be an issue currently. As I have not been able to reproduce any case where the server returns compressors in an order different from the client. But if that behavior changes in the future, we'd be using a lower priority compressor than what the client requested.