What is the best large mammal?

Best what? Best hunter? Best tasting? Best pet?

You said what you said and then tried to explain that you didn't by saying you don't mean a Hippo. So is it which large mammal or which one animal? I pick the Shrinkexpand Whalephant Chihuahua.

Which unanswerable question is the best?  And which unanswerable question is unanswerable because it is totally meaningless?

You cannot be given an objective answer. All answers will be subjective, i.e., people's preferences.

It may have been possible to narrow it down to a small number of large mammals if you had said best at what.

The best for what? For walking across desserts and remembering the locations of water holes, an elephant is best.  For swimming the length of the world's oceans, a whale is probably the best. For farting in mud wallows, it is hard to beat a hippo. For eating with roast potatoes, cow is pretty good. What is 'best' depends on our criteria. There is no independent measure of what is best.

I think Orcas are the best and the actual apex predator of the ocean. They easily kill Great Whites because they are faster, longer, more manuveravle, and way more intelligent. Great Whites just look mean, and are dangerous but they are still just giant fish.

Giant Flemish rabbit 

The globglogabgalab

I'm the largest mammal you'll ever meet son. Come test me and my rock hard abs when you're done foaming over hippo's cheekbone. See you soon.

-The Largest Mammal

The Jesuswhale who ate Jonah.

a whale , they have the biggest part ..

Humans are in the range of "large mammal."  We're all over the globe and have a high population for large mammals.
(Actually, I'd bet that we have a high population for any mammal.  The house mouse might beat us in numbers, and two species of rat are about equal, but those three owe their success to us.)

Blue whales, they may be the largest vertebrates ever [along with a few other baleen whales], the only animals who may have been as big or bigger were ichthyosaurs, but no other vertebrates have come close to that size. 
 
On land i would say palaeoloxodon namadicus. They're extinct but they're the biggest and strongest mammals ever [as far as we know]. 
 Very few land animals got as big and strong as palaeodxodon. No theropoda dinosaur was as strong/big, though some, in groups, may have been able to hunt the mammals. 
The only ornithischian dinosaurs which we have evidence of being as big and strong were maybe some ornithopods. MAYBE. 
 
Sauropods were unquestionably by far the biggest/strongest land animals ever, but aside from them palaeoloxodon may have been unrivalled, and it was definitely unrivalled by other mammals.  

Bears are best.