OP, I have not owned any of the dogs you asked about except the Boxer…In the past I’ve had GSD mixes, and Rottweilers.
Current dog is an 8 1/2 YO Boxer bitch, runt of the litter, she has topped out at 58 lbs. VERY intelligent, easy to train, sticks to me like velcro around the farm. Has had one small “bump” on edge of toe vet excised 2 years ago-no cancers yet, but I know they are prone to that, as well as heart/eye issues (ANY purebred dog breed has certain issues, more than mongrels).
She is very friendly with everyone, UNLESS we don’t know them, or their vehicles. When outside in our large farmyard, she’ll run to vehicles, wagging away-the whole hind end wiggles. If I don’t know who it is-and SHE knows it, too-the hackles are raised and she seems to be a different dog. NO real aggression, but people DO look at her twice. Always been great with kids-always. If memory serves me right, part of the breeds history was as “babysitters” to children in the nursery in the early days of the breed…
When in the home, knocks at the door that surprise me get a “big dog” bark. In fact, the few times she’s done that, I wonder where the big sound is coming from-she sounds like the big Rottie I used to have!
While I’ve never needed her to out and out protect me-as in attack-from something bad, I know she’d be there if I needed her. That’s how loyal she is.
I got her from a small breeder in Maine… If you decide on a Boxer, I would research the breeder carefully-some lines can be high strung, nervous, etc. Watch out for puppy mill pups-INSIST on a home visit!! When I went to visit the home, breeder had Grandma dog, Mom, Aunts, and pups, all socializing around her farm. Spent 3 hours there getting to know everyone before we picked her out.
I would get another Boxer in a heartbeat!!