I can't really comment on the spaniels, I've never owned one, but I do know Newfies. I have had the pleasure of their company for almost a dozen years now. At the moment, I have 3 Newfs, and each of my daughters have a Newf, as well. The key to finding a great Newf is finding a great breeder. A breeder that does all of the health checks and posts them to an open database. Two of my Newfs have OFA Excellent Hips, the third Newf isn't old enough to have his hips tested. OFA is the Orthopedic Foundation for Animals - a database of health records. I do not worry about my dogs having bad hips. A good breeder will have their hearts cleared by a cardiologist before they go to their homes at 10 weeks of age (shouldn't leave their mama before 10 weeks). Even though you don't want to do conformation or performance sports with your dog, choose a breeder that participates in these venues. Conformation to make sure what they are breeding looks like a Newf, performance sports to make sure the Newf can actually do what it's bred to do. These breeders know their lines inside and out and can pick a great puppy for you dependent on your lifestyle (more active versus less active).
What's it like to own a Newf? The downside- You cannot be a house proud individual. You will have slobber on your walls and hair on your floors. Newfies need to be brushed a lot during spring and summer as they shed their downy undercoat - this will prevent mats. A Mars Coat King #20 will pull out a lot of the undercoat making the job much easier. During fall & winter I just brush a couple of times a week to keep the coat looking nice and mat free.
Upside - I love this breed and really won't consider any other breed. I love their gentle demeanor. My two older Newfs (CGC/TDI dogs) go with me to teach 2nd and 3rd graders how to stay safe around dogs with our Bite Prevention Program. I have a 4 year old grandson, all of my Newfs love him. Generally speaking, most Newfs are great with children. They are affectionate, loving dogs that want to be with their people.
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Newfs are easy to train, easy to housebreak, they follow directions well. They are naturally very social dogs. Your Newf would love to go to work with you, btw. They can be active dogs, it just depends on the activity, lol. They aren't long distance runners and they don't like this extreme heat we are having. To maintain a Newfs weight, 1/2 to 1 hour walk every day is sufficient. I walk them early in the morning while we have this heat spell.
This could be an upside or a downside- depends on how you feel about it. Wherever you go with your Newf, people will stop you to ask about your dog or to comment on them. First they want to know if they can pet them. Then they want to know how much they eat, what they weigh, if you have a big house, who your breeder is or if you breed them, how much do they drool, how much do they shed, and then there are stories, people always want to tell you stories about Newfoundlands that they know. A Newf can literally stop traffic!
As adults, they eat about the same amount as a Golden Retriever or Lab. While they are puppies, they can eat as much as 6 cups a day.
Some meds are less expensive, some meds are more expensive. I can treat all three of my Newfs for heartworm/worms for $45 a year. Frontline Plus is more expensive, yes. Supplements are less, I can purchase *human* supplements for them because of their size. Likewise, some prescriptions are less because I can get their prescriptions filled at a pharmacy for $4, again because of their size - they can take human meds.
I'm not trying to sway you one way or another, any dog takes a big commitment on your part, a Newf takes a HUGE commitment. They must be well socialized and well trained while young, that would make your life a whole lot easier.
Newfoundlands steal your heart when you aren't looking, and you'll wonder how you ever got along without one.