I'm going to agree with Ranger here. The size of a SD is an important aspect to consider, but the size needs to fit with the individuals disability. The ONLY time a SD should be carried is when it is necessary for their safety. There are pros and cons for every size of SD. Many PSDs will double as medical alert, mobility, or another type of SD as well as MIs often accompany many other chronic conditions.

The qualities that are so very necessary in a SD and the necessary temperament are not the qualities that are common in the small breeds. Don't get me wrong, I'm not saying that small breeds can't be great SDs, they can. But, the percentage of, say chihuahua or JRTs, that are able to make it in the SD world is MUCH MUCH smaller then Goldens, Labs, GSDs, and the larger breeds. If you check ** (temperament testing) you will see that as a whole, larger breeds have a more stable temperament. So, limiting yourself to the little ones simply because they are easy to carry is going to set yourself up for failure.

My service dog is a medical alert and mobility dog, and is a 115 lb Rott/Aussie mix. Because of the nature of my disability, I will also need a larger dog. I would think that, depending on the nature of the MI, a larger dog would better be able to do the job. The MAIN thing to consider is the job the dog needs to do. A little one may be able to be a great medical alert dog but could not do mobility work.