What a great thread idea!
Bird wise, It would have to be the Eurasian Jay:
Followed by the Great Crested Grebe:
In the insect category, out of the many praying mantises I’ve had, these two incredible leaf mimics have been my favourite.
First, Choeradodis rhomboidea:
and Deroplatys desiccata
TRIGGER WARNING arachnophobes! 
Finally in the spider category, it has to be the Diving Bell Spider, which I’ve been lucky enough to see once in the wild! (this is an underwater shot, the silvery stuff is air trapped around the abdomen. The spider constructs underwater web pocket which it fills with air. The spider often spends its entire life underwater, only returning to the surface to refill its air supply.)
and pretty muchany jumping spider:
Looking forward to seeing what others choose as their favourite animals.