I know they have bad reputations, but a lot of the pit bull + mixes are not super high strung and act very mature. The Grey ones often seem especially calm. They all NEED to be socialized, but they are often very good with kids plus very protective (and fearless). Pits don't feel pain like other dogs, so if a kid pulls their rear or tail, they don't give a crap. Ditto when they get shots at the Vets.
Border Collies are know to be very intelligent, but also very high strung.
Pits (and mixes) are also almost always available for free at any Humane Society place for close to free. They generally have short hair, so they are not cold weather dogs, but that also means they do not shed a lot.
Yea, I know, foolish to judge based on color, right? Well, Guiding Eyes prefers Black Labs, will work with Yellow Labs but you WILL NEVER SEE a Chocolate Lab as a seeing eye dog! Just the facts!