Coming from a California medical school I have come to learn a lot about the California residency programs. Here is the sense I have gotten....
Each program is what it is, meaning, like every other state, there are programs focused on being small, community-based, and there are programs focused on being large, research institutions. You can't go wrong with many California programs, but these are my thoughts on them...
UCSD - I don't know much about it. I have heard that it is great, however, many I have talked to say that their residents aren't very happy and that the pediatrics department has been struggling for decades. Apparently many faculty are constantly threating to leave and UCSD's relationship with San Diego Children's Hospital is on-again, off-again from year to year.
Children's Hospital Orange County - Medium sized, community-based program. I've heard their residents are very happy and they get a great well-rounded education. I've heard some academic pediatricians question the quality of their faculty and their teaching.
UC Irvine - Smaller program. Good reputation, but not the best.
Harbor UCLA - Small, county program. Although it is small, I have heard GREAT things about the program. Apparently the research and teaching are great, given their small size. Residents have a lot of autonomy and are well-prepared for general pediatrics or fellowship training.
CHLA - Large, high-volume program. Residents work harder, longer hours than most programs around the country, but they learn A LOT and the teaching is great! Great research opportunities, however, not a research powerhouse.
UCLA - Definitely its reputation for being a research-heavy institution preceeds it. They have a much lower patient volume than CHLA, and many residents tell me that they learn more from independent study than from actual patient care. Some subspecialties are not represented (eg. pulmonology), but some subspecialties are the best in the world.
USC - Small, county program; not what it used to be. Many subspecialties are not represented. The faculty is decent and very friendly, however, not sure the educational experience is of the highest caliber.
Kaiser Los Angeles - Very small, close-knit program; community-based. Residents tell me that it is very good for general pediatrics training, however, I've heard they aren't the best prepared for fellowship.
Stanford - Large, research-heavy, tertiary care program. I've heard that the residents are well-taught and well-prepared for general pediatrics and fellowship, however, I've heard the patient exposure is VERY tertiary, if not quartenary.
UCSF - Large, research-heavy program. I have heard great things about it, but I don't know a lot.
Children's Oakland - Large, community-based program. Everybody I have talked to seems to regard Oakland as the greatest hidden treasure in the country. Not many people know much about it, but residents love it there and the teaching is apparently phenomenal. Great for general pediatrics and/ or fellowship training.
UC Davis - I don't know anything about it.
I know there are other programs that I didn't mention, but these are the biggest, most well-respected programs to consider. I would say the best programs in California that an East Coaster should consider are... CHLA, Stanford, UCSF, and Oakland; maybe Children's Orange County if you are wanting a community-based program. Though I'm not too impressed, some would insist on including UCLA and Harbor UCLA.