I still call it Twitter... I just don't think "X" works nearly as well in conversation.
Xitter.
As in the Chinese X. Remember how their leader's name is pronounced.
I still always go on the site using twitter.com domain or search.
At least in writing you can use [insert double-stroke X here - which HN can’t display] to make it clear that you mean the social media service. (Unless you’re talking to mathematicians.)