Duh! No way! If one disregards parasites and microbes living inside humans, then the winner is...dogs.
No other life form, big enough to walk around anyway, lets another life form take care of its every need. Humans provide dogs with food, shelter, recreation, and Christmas presents. (We won't mention tooth decay and excessive weight. Like humans, dogs must take the bad with the good!).
Okay, a few earn their keep, like sheep dogs and border collies, but the rest just eat, sleep, bark, crap, wag his or her tail, bark, sleep, eat, bark, lie around with sad eyes (perhaps aware of living in a golden cage), eat, bark, require walking in the rain, stink up the house (hey, it was just out in the rain!), bark (science has proven that dogs bark for no reason...sorta like women and gossip), sleep, eat, require walking in sub-zero temperatures, bark, shake off the rain inside the house, sleep, eat, be unemotional about and ungrateful for Christmas presents...
There could be a downside: if people manage to extinguish human life on this planet, dogs are screwed. They will be incapable of evolving back to wolf-hood and be unable to survive on their own (like teenage children and recently divorced men). They will, nevertheless, still be able to bark...
Prior to writing novels, the author enjoyed a multifaceted career: from decorated combat aviator to advertising professional to global communications director of a major consumer brand. He has traveled the world and met sports, film and television stars, political leaders, and royalty. He graduated from Middlebury College, is married, lives in Germany, and has two grown children.