Just my $0.02. As a first time Gold Coast visitor this winter, with a family of 3 kids aged 10-15, the consensus was Dreamworld was the best, for the following reasons:
* More real "thrill" rides. Dreamworld had 5 (Motor Coaster doesn't count because it was a bit lame, but that still leaves Giant Drop, Tower of Terror, Claw, Wipeout, Cyclone), versus 3 at Movie World (Batwing, Superman, Lethal Weapon) or 2 at Sea World.
* Two of the aforementioned MW rides had a 140 cm limit, which excluded our youngest.
* On the days we went, MW lines were much longer. The Superman Escape broke down for half the day (which I can forgive), but the Lethal Weapon didn't open until noon, which looked like a cost-cutting exercise, but that blew up in their faces when the Superman went down, leaving the lines for these two rides extremely busy, even at the end of the day. Contrast Dreamworld, where we could get in at 9.00 and do ALL thrill rides in an hour or so, and the lines were short enough at the end of the day that we could get a few more rides in the last hour of the day. At Movie World there was only time for one ride on each. Perhaps we caught Movie World on a bad day, but I can only report what happened to us. (There was lots of time for extra rides at Sea World too, but there are only two worth riding. The two water parks also had short wait times, but it's hard to compare them to the others).
* Even to older kids, Wiggles world and Nickolodeon world look cool and bring back memories. They had much less interest in the Movie World themes. (Kids don't watch Looney Tunes anymore, at least mine didn't; they watched Wiggles, and Nickolodeon shows like Timmy Turner and Spongebob).
* Dreamworld lets you take food in, Movie World and Sea World don't.
* Dreamworld/Whitewater world had a special going for winter, in which we could get a 14 day pass for the price of a 2 day pass. So we were able to return for an extra day for free. Again, I realise that's not always the case but I can only report on my own experience.
* Dreamworld negatives would include Q4U people getting on rides ahead of us (but it wasn't busy enough to matter much) and more expensive ride photos (but we didn't buy any anyway).
EDIT: I should add some MW positives. It had far and away the best boat ride (Wild West), and the kids thought Superman Escape was perhaps the best ride of the entire trip. But one ride on the Superman doesn't compare to half a dozen on The Claw or the Giant Drop.