Favorite story? No. Favorite storylines, yes. My favorite storylines are pretty much the main arcs that I've written in the various fandoms. For Darkwing Duck that's my Tension Convention and Like Earth and Water story-verse. I love the Bushroot/Liquidator pairing, and I enjoy playing around in the head canon I have set up around the Darkwing Duck characters as a whole. I'm looking forward into getting into the stuff I have planned but not written/posted yet, as I have plans for other characters that haven't turned up yet. (Loopy McQuack and Camille Chameleon, just to name two.)
For Voltron, it's my Chronicles of a Dark Planet storyline. That's probably obvious considering how much of my writing in that fandom is focused on it, and how even a number of my side stories (like the Doom Fleet: The Boot Camp Years series, for instance) come from that same fanon universe. I'm not ashamed to admit that I love my take on Doom and their society, and all my other OC Doomites that have become a fixture in it, such as the Aldar'ach clan.
For Thundercats, I think I can get a little more specific and say Revival and Path into the Darkness are my favorite stories. They're part of the same universe, but I really enjoyed being able to expand it and do things with other characters and imagine what it might've been like a little bit in the future and past. I enjoyed the way these stories really let me get into the heads of the characters in different settings. It's also fun to write the Lunatacs as semi-good guys. They'll never be "good" (at least, not the six we saw in canon) but in this storyline they're gray area characters and protagonists rather than just the Thundercats' enemies like they were in the show.
And so we've reached the end of the 30-day Q&A session! I hope you've all enjoyed reading my answers as it's gone along. It was a lot of fun to do.