If we go chronologically, they first kiss is in adored SP, but as I know a lot of shippers doesn't consider that thing canon(and who can blame us), so unfortunately in this case kiss doesn't count.
What we have next? In Chakram, no wait blondie killed that one.
Next, if I'm not mistaken is in EB, but wait that was only dream. Very hot dream, but still just a dream. Hell, now I want to listen Nelly's song.
So next we have AUS. For last no problem with this one or I need to say two.
Now you get what I mean? This is hard. So which one you consider Xena/Ares first real kiss?