What Motor Yacht Brand Is The Most Mechanically Reliable?

Don't know where to start. You're not in touch with reality. The commentary here have many hundreds of years of experience. You have zero yet think your going to go do all these things??
Go buy a regular boat with genny and live on it for a few months in a marina. Than try a week on the hook. You'll start to learn everything your up against. Solar will not work with ac. Period.
Those sites you read on the internet are written by dreamers with no formal education or real world experience. All they have is a camera and internet connection. Any engineer including me will rattle off multiple physical impossibilities about your plan. Your going to waste your new found wealth. Think before you jump.

I would say Hatteras, if I had to choose one. They use high quality components in their builds and they have a lot of redundant systems such as 2 fresh water pumps, 2 fuel transfer pumps, and etc. Their wiring and plumbing is done extremely well, and well routed with diagrahms of everything on board every boat. Also their parts are easy to source in the United States. A hatteras is still going to have stuff that fails, but the big difference is whether or not you call Sam's Marine or go to a good local yacht parts place and have the part within a day, or you're waiting weeks to months for it. Or you call the factory and ask where something is located, and someone at the factory will give you the answer right then and there. Azimut or San Lorenzo cannot even tell you where electrical components are located because each boat, the electrical is installed by a different sub contracter and nobody follows the build plans .

Case in point, the wait on a water heater element for a 2019 Sunseeker is close to a month (with no hot water). Same goes for all of the Euro brands with Euro equipment. Need a sea strainer basket, go to your local West Marine. Need one for a Euro boat and it has to be ordered and takes a month or longer to get. Etc. Etc Etc. Need virtually any part for a Euro build and you're waiting a month for it, or longer, or going through the expense of retrofitting a U.S. made part.

Then that makes your entire question of what can be operated by one person mute. You can't operate any of them today and you'll need extensive training, far more than you may realize. I would suggest a professional captain running it for at least the first year and I think most insurers will require it. Even then, operating a boat in that size range alone is very debatable as a strategy for a newbie.

You got the money, it's burning a hole in your pocket, you've fallen in love with the romance of boating, but not yet been exposed to the realities and meanwhile focusing on solar and no generator. You're not going to get the solar you describe on a 50' and can't imagine it on a 75'. Where are you going to find a flybridge with 900 sq ft of roof space. That is 60' x 15' and I don't know any 75' even with a 60' flybridge roof.

Now, you romanticize living full time at anchor. Have you ever spent a day at anchor? A week? A month? I'm afraid you've come up with a fantasy, not a plan. Please spend some time on a boat doing similar things, charter or go with others or do anything to then develop a practical plan. I just see you headed toward an investment in a money pit and putting way too much of what you have available into a boat you won't enjoy and that will quickly be worth far less than you spent on it.

When you jump into something, typically it's best to mimic others for a few years before coming up with a different plan of your own. You may have a better way, but you're not in position to develop it when you don't yet understand the normal way. Do what others do first, learn the standard ways, then go forward with your new and better ideas.

We had years of small boat experience. We went to school and got our captain's licenses, but we still went a very long time without going out without a licensed captain aboard. We didn't yet know what we didn't know. While many do, I still would not operate a boat in the size you're talking about alone. But then I don't swim alone either.

There's an "eye candy" factor, too. Some boats might look nice to you, some might not. One way to get a feel for what might be pleasing is to go walk the docks. Another would be to look at pics on the boat/yacht sales websites. Make a list of good, make a list of bad, etc. You can also get a feel for common features associated with various makes/models.

Probably especially useful to focus on boats made in Europe at first, given you want to be on the Med. That could solve (or at least manage) a "parts availability" tail that comes with boats. (Capt J suggests Hatteras, good brand, don't know that I'd want to go that route living in the Med.)

Also... think service. Your windfall may mean you can hire service, maintenance, repair, etc... but even so, and assuming you'll want to do right by the boat... you (or your minions) will be repairing/replacing/upgrading something every day of your ownership. How's that sound?

You might try chartering for a week or a month or whatever... to get a feel for what it's like to live in a marine environment... that comes with the constraints that accompany all the romantic opportunities most people imagine.

-Chris

Catamarans.
By the way, which Detroit muscle car was the best mechanically? If you think on that a bit you will understand why your question is so hard to answer.

None of them, a new v6 base model mustang would smoke most all of them in every category. And, a new Dodge Demon, corvette z06, Camaro Z28 or Mustang GT, would make all of them look like grandma's grocery getter in any performance category. LOLOLOL

What's wrong with grandma's grocery getter??

No challenge. Just have a 100 foot barge covered in solar follow you around.

The biggest. The biggest yachts have the biggest deck space. Is this a trick question?

E-type Series 1 is perhaps the best car design ever.

Which brands of Italian yachts have excellent electrical?

For sure. I was trying to reconcile or figure out from the OP, who is a professed old Detroit muscle fan, why he is interested in " the most mechanically sound yacht"?

The OP has yet to explain this strange disconnect.

Our AB does and our Riva's do.

Now, I don't think outside Azimut, the issue is the electrical on the boat, but the access to replacement parts. Fortunately Ferretti Group keeps a good inventory. On the AB, we've purchased enough to have our own supplies.

I love the concept, but you do realize, don't you, that they have generators, very large ones. A Silent 60 has a 100 kW to a 145 kW generator and carries 1000-1900 liters of diesel. So they clearly do not meet the requirements you set forth in your posts.