I like just about any Orthrus hybrids that take on the double heads, with a special place in my heart for the Jade Hound. I also like the Fragmented Dragon. Now that I think about it, I like most level 48 pet hybrids, including Lifezilla, Mythzilla, Grimzilla, Basilisk, Traveller, Maelstrom Oni, Archfiend, and many more.
I think what made those specific hybrids so special was how hard it was (and still can be) to obtain them. Unlike the level 58 pets, there is not a 100% chance of receiving a hybrid. It also depended on what school your pet was. So as a Life wizard (with Satyr) trying to hatch with Myth wizards (with Orthrus), I was much more likely to get a Satyr or Traveller than a Jade Hound.
My favorite looking one is the Dapper Corgi. I find my Dapper Corgi really adorable, but stat wise, he isn't really good for me, because he is a pet, therefore gives me blades, which do not come in handy for a wizard. I also love how adorable the Lil' Siren pet is. I wish I had it, but nobody will hatch with me. They will either decline the request, not have enough gold, or not have an adult pet. Bt until then, I will sty with my Dapper Corgi.