The way I see it, both games are games that encourage creativity and imagination, just in different ways.
FeralHeart gives you the freedom to make your own meshes, custom markings, presets, and even entire maps that could pertain to either realistic or fantasy design, and this is where it is a superior game to Arokai. However, moderation of trouble-makers isn't all that great and people are repetitively exposed to some pretty obscene language, which may not affect some, but bother others. Besides that, the game's top administrators, especially the game-maker himself, are incredibly hard to gain contact with, which has been a problem to many...
Arokai gives you the freedom of multiple marking-layers, which definitely is superior to FeralHeart where you'd have to make a preset from scratch just to have a tiger with scars. It also has a variety of animals to choose from as well as planned items, such as armor. However, the game having presets is skeptical, and map-making and mesh-making are entirely out of the question. This means that there will be a bigger concentration of people within maps, which could be overwhelming for any mods...