As others have said, this really depends on your family and what you want.
My family (myself, DW, and on our last trip for the first time, DD who is now 2) do not like resort days. I can see why some people do and if we were going for more than a week (almost every trip we take is 8 nights, occasionally 7 or 9) or lived close by we might even try it out. But after a particularly go go go trip that we took with some extended family once DW and I have taken a much more relaxed approach. We aren't going to be speed walking across the park to try and be 2 spots closer in a line. And, even before DD was born, the two of us would take midday breaks.
We usually go in either March or November/December, DW is a teacher and summer is just too hot, and while some trips have been too cold for the pool there have been numerous instances where you could find us at one of the quiet pools after a day in the parks. DD was 11 months old on the last trip and even though she was a very good traveler and took naps in her stroller, it was also good to get her out of the sun for a few hours each day, but doing that AND taking a whole day off from the parks just strikes us as too much time spent not doing what we went to Disney World to do. Our neighborhood pool is great, and DWs parents live nearby and have a pool too, so that's no loss for us.
There is so much to see and do at each park that we just prefer having at least 1 and a half if not 2 days per (when park hopping was normal). I didn't look at all the replies so if this has been said I apologize, but during our last trip and planning for our upcoming trip next March, have you looked at just how much (or little) your youngest can do at Hollywood Studios. DW and I love that park and the thrill rides but on our last trip DD could only ride Mickey and Minnie which had just opened, and Toy Story Midway Mania. As much as DW and I love the rides in that park we are seriously considering doing only a half-day there for our next trip because even then, DD may only be able to ride 1-2 more things at most. She is on the petite side, though, so maybe your youngest can do a bit more.