Short answer
How do you choose a plumber in Santa Ana?
Match the specialty to the job, check the CSLB license yourself, and insist on a diagnosis before a price. For a repipe, use a repipe specialist. For a slab leak, use someone who locates before they cut. Then get the scope in writing with the exclusions stated.
What we judged them on
These are the criteria, stated before the list rather than after it, so you can disagree with them and form your own view. They're also the criteria worth applying to any company you find yourself, including the ones not on this page.
A license you can check
A current CSLB license, in a classification that covers the work, under the name on the quote. California requires a licensee to print its number in its own advertising, so a company that hides it is telling you something.
Specialty that matches the job
A repipe specialist and a general plumber aren't interchangeable. For a whole house galvanized replacement you want the company that does it every week. For a mixed job you want a generalist.
Diagnosis before a price
Anyone quoting a slab leak repair without locating the leak first, or a sewer repair without a camera, is guessing at your expense.
Pricing you can compare
Written scope, itemized, with exclusions stated. On a repipe that means saying whether drywall patching is in. On a water heater it means saying whether the permit is in.
Permits pulled as standard
A contractor who suggests skipping the permit is saving themselves time and handing you a problem at resale.
Reachable when you need them
Emergency response is a real differentiator in this county, particularly during the first storms of the wet season when everyone is busy at once.