The best plant to breed in the beginning is the one that comes from the round green seed (the foliage looks somewhat like rosemary). It sells for more than $40 per plant. I usually keep breeding that plant over and over until I can afford the soil upgrade. Upgrading the soil is what allows you to breed the more fragile (and more valuable) hybrids. Don't upgrade the water or fountains until you've upgraded the soil if you want to make more money more quickly.