Hmmm... I think I would choose either Corehound Pup, Winterspring Cub, or Dark Whelpling (in that order), as that was my original 3 level 25s.
On the offchance that they're all taken then I would choose Amethyst Spiderling. Mine is called Spiderpig. Why? Why not?
If I'm really really unlucky then Tiny Harvester.
Note to self: You have about 20 pets that need names. Get on with it!!