I got my first Connemara pony 5 years ago after having Paints and WB (my daughter did eventing.)
I now have 3 with another due in May. I find them to be very friendly, athletic, and versatile. They make great family ponies and really fit in to so many styles of riding: eventing, jumpers, driving, dressage, trail, and western events. They are just a great all around pony with a good attitude who wants to please. Size is 13’2"-14"2+ for the purebreds.
The only Fjord I met was stubborn- Mostly ridden by kids and wanted to get away with taking you where she wanted to go.
My mustang looked very much like a Haflinger- very very lazy, but a bit stubborn and temperamental. She did not believe in working unless you make her.
Hackneys- very hot and forward moving horses. I have a Shetland pony I’m training that probably has some Hackney in him. They eventually want to train him to drive, but he is very hot/forward. He has a good work ethic and will go all day with the kids. Not very patient - he likes to move!
I bred my mare to a Connemara. My mare is super calm and quiet and I wanted to complement that.
Caspian horses- I met someone who drives and is breeding them. Small, quiet, and good natured. I don’t recall the name of the breeder.
I agree with the Fjords, that is my experience also. 
A word of caution if you keep your mare on pasture. I know many people who got a mini or pony as a companion for their riding horse then had to take it off the grass when it got too fat. Then it also needed a companion and so did their other horse. So beware of the multiplying effect! Maybe better to get a small horse.
