Mr P suggested that I roll dice to figure out which to work on next. Then I thought, hey, better than rolling dice: asking actual readers! The people I'm doing this for!
You can read excerpts from some of these to help you decide.
Which project should Antenna finish next?
Ars Draconis part 3: Dragon's Heart (the sword one)
Post-Grave h/c tagfic (Giles/Buffy, the sweet newage one)
Tradition & Protocol part 1 (Giles/Buffy, the bodyart one)
"January Weekend", Giles/Ethan, story of how they met, in the universe of the Christian bond story
"Reconnection" part 3, even though I'm stuck on it and might take a while to figure it out
Note that the first three would probably be complete in the next week or two. The others would take longer.