What is your priority? Maximum entertainment or lower crowds. Not as cut and dry as usual this year. Normally, week before Easter for maximum entertainment (and heavy crowds), early June for low crowds (and shorter hours, and less entertainment).
Everything is different this year (and probably next year too) though. With the refurb schedules the way they are this year and the new rides opening up June 3 and the new parade starting Memorial Day weekend, it's much harder to say. You will get lots of crowds the week before Easter, longer hours, and more entertainment, but still no parade, no Star Tours, and no Splash Mountain. Without those activities to absorb some of the crowds,
Disneyland is likely to feel even more crowded. Normally early June would be a low crowd time, but with the new attractions opening, that might mean a big surge of crowds. Now, if everyone's waiting in line for those new attractions, Star Tours and Little Mermaid, and sitting for hours waiting for the new parade, and those aren't going to be your priorities, the rest of the park may be fine, better than April.