This question can have two very simple answers. If you are looking for one of the tallest dogs it is either a Great Dane or a Irish Wolfhound. But the largest dogs are the English Mastiffs, which usually always weigh above 200 pounds.
Either a gret dane or a wolfhound newfoundlands are large as well and if you live near water that would be great they are usually water rescue dogs. Do a web search on large dog breeds and it will give all of them to you so you will be able to make informed choices.
