On the parent site there are (at this moment) 37 questions tagged with 10.04tagged with 10.04 and 9 questions tagged with lucidtagged with lucid. Of the 37 questions tagged with 10.04, 5 are also tagged lucid and 1 is also tagged lucid-lynx.
It looks like thus far 10.04 is the popular choice and I see also the top voted answer to this related question.
I think it would make sense for the other two to be suggested as synonyms for 10.04synonyms for 10.04. However, that decision is in the hands of the +1000 users (currently 7) or the moderators (I think).