We liked the 5:00 show because you can then go to MK for the evening parade and fireworks. We take the boat from MK to get to the Fort. It makes for a very nice evening.
It really depends on what else you have planned that day.
You need to allow at least 90 mins travel time, so the 5pm show can interrupt your park time.
The 7pm show I find a hassle getting to because the boat dock is PACKED from all the people who are just getting out of the 5pm show and all the people going to the BBQ (if there is one that evening).
I think the 5pm one is just easier for transportation.
I've personally never had a choice of time slots. It fills up so fast I take which ever one is available.
We prefer the 5pm one as well. There's a lot of food and the earlier show gives you time to walk around after the show, digest and possibly see parade/fireworks. Hoop-Dee-Doo is one of our favs... hope you have a blast!!!