We are also in California and had the same question. I can't tell you which is better - a custodian account or 529 - assuming you are the one managing it.
With no tax benefit to us, we opted to have my wife's parents open up the 529 account for our children through Vanguard. The grandparents do receive a tax benefit in their state. Also, it helps our children because a 529 managed by the grandparents does not count towards assets for Financial Aid, though it would count if we managed the 529. Also, they're
So, this doesn't directly answer your question but might offer you an idea on how you could optimize your situation by thinking outside the box.
Another consideration is that a Roth IRA allows you to take out money penalty free prior to 59.5 years of age, if it is used for your childrens' college costs.