I don't know if there's a thread on this, but oh well.
Well, my favorites would be Diamond (epic and baby are awesome), Fairy (I actually like this one), Eagle, Familiar, Infinity, Firestorm, and Poison.
Diamond is awesome, I really like Diamond, Rainbow, and Unicorn. Fairy is okay, but I like Fairy, Mistmoth, Virgo, Seahorse, and Eclipse. Eagle is not my favorite but I like Parakeet and Angel (<3). Familiar and Nano are definitely awesome. Infinity is really cool too. Firestorm base I only like for epic form and some baby forms. Poison is cool for stuff like Patchwork.
Least favorites, well probably Island (bubble is ok tho), Coral (except for ****erwhale <3), Fire (hate the second stage), Fruitful, Trickster, and Wild (only for the third stage).
Tiny seems to be based off of Coral as a baby, second stage is based off of baby Island. The epic stage is based off of Life.