Regarding breeds that are good for counterbalance and balance assist, height will probably be a factor. As far as I know, there isn't a really good balance harness design for shorter dogs yet, that doesn't put a lot of extra strain on their shoulders while they are working. If anybody does know of one it'd be good to hear about it though!
I'd look at breeds with typically good joints, temperament, health, and longevity like standard poodles, collies (some individuals are around 26"-27"), spinone italiano, gordon setters, etc. Some of the big sighthounds excel at balance and mobility assist, such as borzois. Some individual greyhounds can have the right temperament for SD work as well.
There are also more traditional SD breeds, such as german shepherds, labs, and golden retrievers. Dobermans and rottweilers can produce good prospects as well. I recommend being cautious looking for prospects of those breeds because there is such a huge variety of temperaments, and some lines tend toward catastrophic health failure (early cancers, joint failures, etc.) but there are some really great dogs out there.
I'd look at breeds with typically good joints, temperament, health, and longevity like standard poodles, collies (some individuals are around 26"-27"), spinone italiano, gordon setters, etc. Some of the big sighthounds excel at balance and mobility assist, such as borzois. Some individual greyhounds can have the right temperament for SD work as well.
There are also more traditional SD breeds, such as german shepherds, labs, and golden retrievers. Dobermans and rottweilers can produce good prospects as well. I recommend being cautious looking for prospects of those breeds because there is such a huge variety of temperaments, and some lines tend toward catastrophic health failure (early cancers, joint failures, etc.) but there are some really great dogs out there.