Hollywood studios is currently undergoing one of the biggest "re-imagineering" of all the parks for ages - there are very few actual rides left there at the moment.
Animal kingdom however has just undergone one and has the whole new Avatar area with brand new rides. But, for us out of the 3 non-magic kingdom parks, Epcot wins.
We bought the 14 day passes - because we wanted to dip in and out of the parks at will.
The 14 day passes allowed us to nip to Epcot, say, at opening, leave at 1, go off park for lunch, then go play mini-golf (included in the ticket) then nip to Magic kingdom for the fireworks - only 1 lot of parking to pay for the day, out of the parks when they are busiest, and a bit of fun too.
The 14 day passes also include the Disney waterparks - nip for a swim in the morning before going off shopping, then fireworks in the evening...
and Memory maker - so you can download all your ride/photopass photographer(all round the parks) photos for free.
The 14 day one just meant for us that we had that freedom - go where we wanted, when we wanted, and if a park got too busy, go elsewhere - didn't feel like we had to stick around to get our money's worth like we would have with a single park single day ticket.