I'd recommend a few things. First off, Education.com has a bunch of helpful articles about choosing a good preschool (located below). Also, I'd ask parents in the area you live in for advice as well. Finally, I'd visit the schools to get a first hand account of what feels right to you.
Home is the best preschool; however, if you are unable to provide a preschool education and take advantage of the great parent/child bonding opportunity, I would check with other local parents to see what they suggest. Some elementary schools offer preschool and that would be a great place to start as this will be funded by the state, will have certified teachers and will familiarize your child with the school that he/she will attend at a later time.
Qualities I would look for is a clean, safe, loving environment with either a trustworthy, mature adult who has "a way" with children OR a certified teacher who is also trustworthy and mature. I would want someone who will teach the basic skills and also teach by example with high morals, values, good behavior, manners and take an individual interest in my child's safety and well-being. You may want to speak with a homeschooling Mom and see if she would be willing or able to add your child in her home.
Best wishes and I hope you find a great place for your preschool child to develop their love for education.