To be quite frank that is entirely up to you!
What I'll do here is give you "MY" thought process with regards to length of stay. For me, I look to schedule between 3 to 5 nights. I appreciate that is a broad time (and some might say "short") period but there are several issues that dictate that. In the end the primary driver is finances, second to that is "where" I'm looking to stay. Weather can also play a role in how long you stay. Its cooler in the spring, which does make it easier to get around. The summer in Florida is quite hot, which can make being outside difficult for some.
For my first on-property visit it was my family of 4 ( 2 adults and 2 children). We booked 4 nights at the Moderate priced Port Orleans resort (this was before Dixie Landings came under the POR umbrella). We visited in late April so this did require taking our children out of school, so parents keep that in mind too. Being our first visit we wanted to stay on-site but didn't have the funds for a deluxe resort. Our children where 8 and 6 years old at the time so 1 day per WDW parks was our plan. It worked great.
For our most recent visit, I scheduled a 3 night / 4 day surprise stay at the Deluxe Yacht Club resort close to the Memorial Day holiday. Our late May visit saw temperatures in the high 80's through mid 90's, it was hot but that made the pool even sweeter!. The short time frame was dictated by my desire to stay at a deluxe resort, available funds, and our job responsibilities (Donna operates her own business so being away for a longer period of time can be problematic). This did require some planning in terms of park visits, where we had to split time (between 2 days) in Epcot, which worked out because we could walk there from the Yacht Club. In the end the point of the visit was a break for Donna and even with the short stay it was still a magical vacation.
I know others who plan a least a 7 nights for each visit. I'm a huge proponent of down time during a WDW visit. For me that usually means at least 1 afternoon at the resort pool. A longer visit allows you to plan a "complete" down day at your particular resort. Others use the extended stay visit to explore off-site parks such as Universal (Harry Potter's world is the big draw).
In the end how long you choose to stay at WDW is a personal choice that involves several important questions:
- When are you planning on visiting?
- How much money are you willing to spend?
- How much vacation time from work do you have to use?
- Are you traveling with young children?
- Is WDW the only location in your plans?
- Are you looking to plan a "full" down day?
For our September 2014 trip we're staying 4 nights / 5 days. This means one park a day and two afternoons of downtime. But this is just me.......................