WolfQuest is best for realism, but horrible for roleplay...er, attempts at roleplay. But of course, it wasn't made for roleplay so much as educating people about wolves.
FeralHeart's a lot more flexible when it comes to pretty much anything - feline or canine base, markings, wings or not, etcetera.
It really just depends on your taste/mood.
Sometimes I prefer WolfQuest (single player of course ._.), sometimes FeralHeart. But I had to uninstall WolfQuest recently because our computer was acting up. WolfQuest gets a bit old after a while as their updates are few an far between in comparison to most games. Sometimes the lack of any type of 'goal' turns me away from FeralHeart, but I've been in a roleplaying mood lately. xD