On our first trip in 2008, the boys were 1 and 3. We only stayed 5 nights and we got a 5-day ticket. We arrived at WDW around 11:00, checked in (room was ready so dropped off luggage in there) and had lunch at Pop Century. We headed to MK on the bus, and got there about 1:30. We had a nice afternoon, and we went to all the "anytime activities" that didn't have a wait. Now you can FP+ rides! which is even better because you can go on 3 more popular rides. Anyway, we spent one day at each of the other parks, and an extra day at MK. It worked well for us when the boys were very little.
On our 2010, 2012 and this upcoming trip, we have 2 and a half days at Epcot. We love the restaurants there and just spending time in the countries in general, so we feel like it's nice to have more time. We also became DVC members in September 2008, and our home resort is BWV, where we always stay. Epcot is just a short walk away and we enter through the International Gateway. Makes it very easy when returning to Epcot for dinner at one of the countries. We stay 10 nights now, ever since the 2010 trip. We spend 7 days at the parks...3 at Epcot (one is a half day with just the countries and eating, but now some FP+ attractions since we can!), 2 full days at MK, and 2 full days at DHS. We haven't been back to AK since our trip in 2008. It just didn't appeal to us much. It was nice and all, and perhaps we will go back there again in the future if the kids want to, but we always ask them and they'd rather spend more time at one of the other parks. We are also going to Legoland one day, and we have a couple of days without a theme park so we could just sleep in, swim, and do whatever we feel like doing without having a plan. We always schedule a couple of days like this, and we find it makes the vacation much more relaxing.