We just got off of the 3-day and at the end all we kept saying was that we wished we had one more day. SO, I would definitely go for the 4-day cruise. This way you get one entire day at sea to enjoy the ship. Yes, a 7-day would be great (I, myself, am attempting to save up for one of theses), but if a shorter cruise is all you can afford right now, go Disney. My dad wanted nothing to do with the cruise when we first came up with the big family trip. By the time the cruise was over, he was ready to book another one and is still talking about it. And my mom thanked me for putting together our family cruise before the ship even left the dock. I say if 3 or 4 days are all you can do now, go for it. Disney makes it worth it and I am going to guess that no matter how long your cruise is, it won't seem long enough.