We like early June or late May best. The water is warmer, and it is a little less crowded. But the usual places are open. There is a little less high wind in our experience, but we have never encountered a north swell at that time. The air temperature is also warmer (however with AC that's not an issue, and we survived no AC our first time in early June).

Of course we aren't very experienced, but have been in January, March and May/June a few times. So perhaps others can correct me.

I'd say you don't need to change plans much between March and June.