obviously depends on wht you want, but we did the dune buggies two weeks ago and had a lot of fun.
On the dune buggy trip you leave around 10:30 - 11:00, drive dune buggies down a sand/dirt/rock road for an hour or so, hang out at the beach for an hour or so then have lunch at the beach. After lunch, back in the dune buggies to see some small ruins, then back into town the way you came.
A quiet, relaxing day it isn't, but if you want to bouce around, it's a fun way to spend the afternoon. Be warned, it is a bumpy ride, and the back seats are better for kids. THe disney trip is not dune buggies, but jeeps. Same road I think (we saw some along the way), but a calmer, more comfy ride, but probably not as much fun. The dune buggy co is more free and easy on their restrictions. Disney trip is for people over 10 years old, my 5 and 7 year olds had a great time bouncing around in the dune buggies.