Mammals are my favorite group of animals, with elephants being my all-time favorites, and ungulates (rhinos and takins specifically) following.
Birds come in a close second, with hornbills, Birds-of-Paradise, Birds of Prey, Gruiformes and Ciconiiformes being my favorite kinds.
I'd say reptiles and fish are just about tied; boas and crocodilians are my favorite reptiles, while I find fish in general to be extremely fascinating.
Amphibians and invertebrates are tied for "last" (however, there really is no last place when I love all animals). I don't really know much about amphibians, so I guess frogs (vague, I know) are my favorites. With insects, I've always loved caterpillars in particular for some reason, but recently I've "fallen in love" with the large number of tremendous invertebrates that can be found in the world's oceans.
And since when were plants and fungi animals?
EDIT: I actually honestly don't know whether I like mammals more than birds (as a whole). With mammals, I don't really find rodents, lagomorphs, bats, etc. as interesting as ungulates, canines, felines, whereas with birds I really enjoy seeing any type. Of course, should a rabbit or some insectivorian show up in my backyard, I would watch it for hours until it left, but you get my gist.