I have no thought of asking for the Democratic ballot. Clinton is an authoritarian, corrupt, and a dynastic candidate with an appalling sense of entitlement; on the other hand, Sanders is a socialist, and I don't vote for fascists or socialists.
I'd have to register soon (if it's still possible) to vote in the Republican primary; they don't take independent voters in California. The idea of voting against Trump is not without appeal; see my comment about Sanders. His rival is Cruz, and some of Cruz's positions appeal to me; I'd like to see if he carried through on his proposal to abolish multiple executive departments and agencies. Also, I'd much rather have him appointing the next few Supreme Court justices than any of the other three. On the other hand, Cruz's views on abortion and same-sex marriage are big reasons not to support him, and those are issues I care about. It's also worth keeping in mind that so many Californians will vote in the Republican primary that my vote will fall into the margin of error in any case.
The other option is to ask for the Libertarian primary ballot. That's a party that's a closer fit to my own views; their candidates have meaningful differences; and also, my vote will fall short of significance by a smaller factor, since rather fewer people vote Libertarian. And since I'll probably vote for the Libertarian in November, it makes some difference to me which one it is.