It would depend on what size class animals you are talking about. A truly large animal like a rhino, hippo or elephant is indeed very strong, but you also have to factor in how much of the animal’s strength is devoted to simply supporting its own body. This sort of comparison is very difficult to undertake; for instance, the wolverine is considered to be incredibly strong for its size – but if you scaled one up to the dimensions of an African elephant, chances are it would be no stronger (though a good bit deadlier with its teeth and claws!). At that point much of its strength would be vested in supporting its massive bulk. On the flip side there are insects and invertebrates like ants – pound for pound (or gram for gram in their world) they are much stronger than most mammals and terrestrial vertebrates.
A human. We have wiped out half the species of animal on earth since we showed up on this planet. Think about it. The humans will and need to survive and our use of tools and brain power alone are enough to wipe out any animal one on one. Plus the damage the human body can with stand is just unbelievable. I’d hands down vote for a human (namely myself) against any animal anyday.