It's important to consider more than just the build quality. Construction crews are generally recycled across builders, and individual superintendents at each builder will matter more to the construction of your home than the builder itself. Good builders can produce horrible phases, and bad builders can produce decent phases.
That said, if you do enter a purchase agreement with a builder, make sure you develop a good working relationship with the superintendents.
Also, the warranty policies and handling of claims can make or break the new home buying/living experience. KB homes may produce some decent products, but their customer service and warranty procedures have resulted in a HORRIBLE reputation.
If I were to rank the builders on your list based on OVERALL quality (initial build, warranty, customer service, design), it would be:
1 - Taylor Morrison (sales, construction, warranty all above average)
2 - William Lyon (some have had issues with customer service, but generally good)
3 - Irvine Pacific (good product, but very limited design center/infrastructure flexibility, and very cookie cutter homes)
4 - KB (customer service and warranty handling are a deal breaker for me)
Good luck.