Unless they are very sick and obviously in pain I would let them live where they are comfortable, which is with me where they have been most of their life.
Now I did have to put down my one dog several years ago , he stopped being able to even stand up or move on his own. The humane thing to do was put my poor guy out of his misery so I found a vet who made home calls and they euthanised him on his favorite spot on the couch surrounded by his loving family.