Still undecided - how to best to Disneyland and Universal Hollywood

I've read and thought about so many different ideas that I'm starting to lose track of what's best for us. Any personal experience or guidance is really appreciated.

I'm looking to take the family, 2 adults and 2 kids 7-10, to California in early June. We love Nintendo and Harry Potter, so at least one day in Universal is a must. But Disney is a big focus.

At first I was thinking 2 days at Disneyland, 1 day at Universal with early Mario access, and 1 day at a beach or park. But the transportation from Disneyland, where I'd assume we were staying near but offsite at, to Hollywood has been stressful if we don't want a car. I keep hearing Universal is a single day affair, but is it worth doing 2 Disney days, and 2 Universal days, and then transferring hotels halfway through the trip?

I just can't make my mind up on how to do this best, thanks again for any input. We LOVED our 4 day Disney World trip two years ago and they'll be over the moon excited to hit up Disneyland.