In order not to hi-jack the other thread, I have started a new thread.
Selecting a breed of service dog really depends more on the dogs personality. Some breeds are more easily trained than others. Training your own dog is allowed under ADA. I think it is good because my dogs know my voice only, can discern my commands even when my cognition is poor, and they bond in a relationship that never has to be broken. Also, as each MSer's needs might vary, each MSer's dog can be "customized" for the MSer.
For me, as long as I am walking, I will stick with the English Mastiff because they are easily trained, they weigh more than me, and they are "my speed". They are also inexpensive to feed because they do not handle a high protein diet well after they get above 40-50 pounds. Cheap, low protein food is best for them due to their slow metabolism.
If I am restricted to a power chair, I would go for a lap dog of not more than 25 pounds. They would function as my "gopher" to open doors and retrieve objects. For these, I know a school in Arizona whose founder has had a long history of training various breeds including dogs of questionable pedigree.
Personality traits are important. We have two white boxers at home. The male is deaf and his sister is quite intelligent, however, both have ADHD. This would be a trait to avoid. A poodle is quite intelligent and I had both a small poodle and a standard poodle. For walking, the standard poodle would be an excellent choice, I think.
Hygiene is another factor to consider. When my service dogs are working, they get a bath once a week. This is also a factor to consider when you have physical limitations. My dogs will happily go to the tub, climb in, and soak (they do not like to get out of the bath!). The white female boxer would not work because she has some skin allergies and bathing is not her favorite thing!
Without any breed bias, you can find breeds listed by their typical disposition. With this in mind, you should still look at the dog and see if they are aggressive or shy. My female English Mastiff is shy. It has taken a lot of work to get her going, but she is maturing and getting better. Some shyness is good because they are more alert to the environment, I think. Too aggressive does not fit well into a social setting. My dogs will go into a restaurant with me, lie under the table, and never "beg" for food.
If your dog is going to be working, you have to plan on their retirement. My first service dog retired at 8.5 years. He worked full-time from 18 months of age. His health has gotten better since his retirement and he thoroughly enjoys his freedom. He still likes to "get dressed" and be ready to work. It has been a natural transition to have the second Mastiff take over. She knows he is Alpha, but when it is just the two of us, she relishes her leadership position.
Lastly, before this gets too long, the breed you choose should be able to live in your climate or your environment. I "hibernate" in the summer, which pleases my Mastiffs because they would rather avoid the hot sun.
Overall, a service dog can provide non-bias, unconditional love and support. Many MSers can regain their freedom. I know for me they have made a difference. It is not every day, but on days when I would not be able to walk, their tugging me along makes my day work. They are God's four legged angels.