This is a very personal one that only you can answer.
We are fortunate in that our Son’s school grant him 10 days leave every 6 or 7 years when we can afford to go back to Florida. We match this up with the October half term week and so end up with 3 weeks for our holiday.
This also suits us perfectly because in that 3 weeks, we get to sample Halloween at Disney including MNSSHP and almost overnight following Halloween, Christmas descends and we can also sample MVMCP. Also at this time we get the EPCOT Food & Wine Festival
You’ll find loads of advice (some helpful) on when to go. Remember though, even when the crowds are high, the parks are great at bringing in additional staff & entertainments so don’t worry that you’ll end up just queuing all day. You’ll still have a good time.
I have used Passporter to help plan our trips before and they have an excellent chart in their “Live Guide” that overlays the Disney charging rates over the calendar, the weather, crowd levels, public holidays and so on. Worth subscribing to view this alone.
Alternatively, there’s a good page on weather levels here
Pick when you want to go and then start your research. If you think of going over Christmas, you may just want to watch some YouTube Videos on crowd levels first, they can be very busy days at the parks.
When you have rough dates in mind, have a think about whether that date will be affordable or whether it is worth leaving it another 12 months to give you extra planning and saving time.
Our latest holiday to Florida started planning in Spring of 2017 for travelling in October 2018. It masy seem like a long time to wait but we were very prepared and it gave us plenty of time to save up to be able to afford to do everything we wanted to do.