I came to this forum specifically looking for this. Dan gets to decide how his characters will answer the question, no matter what we think or want. But only we get to choose what we want to transform into. Rather than just one (albeit very good) imagination, I'd like to see what transformations a thousand imaginations unleashed can come up with.
Personally I love the idea of fairy dolls. I'd probably go with an even smaller version of either Shanghai or Hourai from the Touhou series. Flight, tiny size, and minor magical ability would be tons of fun. I already enjoy building RC models for FPV (first-person view) adventures in a tiny world, but being able to sit in the cockpit of my Spitfire or Panzer III and actually fly/drive it myself would be SO much better.