I have a Paint mare I'm considering breeding as well. I looked at paint stallions and promptly dismissed most of them. I thought about crossing her with a thoroughbred but #1) too big #2) often hot tempered, or likely to have lameness problems. Although it would probably be a nice cross... I don't want a huge horse.
I would not even consider a QH- they are too popular, often downhill.
I've pretty much decided that I will out cross my mare with either a Connemara or an old style Morgan. I think it will improve her topline, and give you a more evenly balanced horse. Some German Riding ponies are nice as well.
i would love to find a paint stallion with a level or uphill topline, and good jumping ability. But they are being so exclusively bred to be identical to the quarter horse. Honestly, I don't know what breeders are thinking. Most Paints are very downhill, as are most Quarter Horses. I'm seeing a trend for super straight hind legs, and I can't imagine that is healthy either.
If I was breeding for APHA registration, i would probably outcross to a thoroughbred or look for a paint stallion with some thoroughbred blood and a more even topline.