It's best to use
https://counterwallet.co as that serves as a "dispatcher" for available CW servers.
CW03 has the new code, but soon all CW* servers should have it. However if your referrals are related to some new CW functionality and you need to do it *now*, then send them to cw03.
If you think they should get some idea of what Counterparty is about and they don't like to read:
https://www.counterparty.co/videos/Thank you! I appreciate it.