If it were just up to me (and it is not), I would spend winters in Michigan through February, and then hit the Florida state parks just for March and April. It's the length of Michigan winters that annoys me. March winds come in April, April showers come in May, and May's flowers are not 100-% safe from frost until almost Memorial Day.
But everything starts to green up nicely in Florida in March, and reservations at the more popular state parks are more easily obtained in April after many snowbirds have gone home to do their income taxes.