If you want maximum stars and skills, crosses might be harder to breed right.
Start off with a mare (mixed or pure) that has 100 BLUP and the highest GP possible. Unless the GP is really good, you'll probably want to use tears because people don't tend to buy mixes unless their skills are really good. When you pick a stallion, it might be smarter to pick the breed with the greatest amount of stars. Try and choose which skills you want maxed out in the baby before you pick your mare and stallion. (EXAMPLE: If you want a high speed horse, crossing a paint and a mustang/thoroughbred would be good)

Hope this helps!