Hm... I think the answer is kind of obvoius, at least in my case. Well, it my own original species that I like best - Shata'lin to be precise - they fall into reptilian-mammal hybrid anthros, not based on any specific species. Second are reptilian creatures of almost all kinds. Third - bird-like races I guess.
I prefer Imaginary species that look like they COULD be real ... be them feral, anthropomorphic or uber-chimerized. (Best Qualities of multiple animal types, such as Dragons, Gryphons, etc.)
For me, that means NOT having strange or seemingly senseless features such as fur patterns which display impossibly specific patterns not explainable through evolutionary logic, or "SPIKES" where a creature has no business having them. (Sorry Lucario ... but that chest spike just doesn't make any sense)
It's all about aesthetic balance, functional feasibility, and an overall balance leaning more towards the believable side of the creatures "Suspension of Disbelief" in relation to it's potential actual existence.
If it's just too weird to believe, I tend not to like it very much ... but if someone can make me almost believe that a flying, winged BunnyBird like the one they created could actually exist ... consider me impressed.
It was more in reaction to your option-destroying sub-note to one of the offered answers.
* "Something based on real animals ..."
(I would have selected this option if not for this foolish extra condition)
".... like a big cat with spikes!"
NO NO NO NO NO!!!!
Spikes coming out here and there for no logical, sensible, explainable or functional reason other than to make the creature look FANTASY-ish is STUPID to me.
If it looks like it could be a real sub-species of feline that either has not been discovered yet, or perhaps once existed but has since gone extinct, or evolved in an extreme environment ... THAT is COOL.
If it looks so absurd that it's clear no such animal has, nor ever COULD exist or survive ... it's just awkward and weird.
There are very good reasons why mammals don't have giant 15 inch bone spikes coming out of their elbows and spines. They would be such a daily encumbrance that such a creature could not possibly survive beyond a singe generation or two. ... Unable to even lay down on their backs, become intimate with another of their species without impaling them, and incapable of passing through any kind of underbrush or encumbrance without getting hopelessly tangled or snagged in it ...
Mother nature knows what she has been doing by NOT creating animals that way.
The modern pooka/Púca (I like the shape-shifters). And I also like alien species( dragons and many other creatures sometimes fall into that category depending on the settings.) And I like genetically made gryphons. And creatures that don't look like robots but really are robots. I like sci-fi type species.