I vote for Margaritaville. I thought the kids menu was superb. My son got the Cheeseburger in Paradise and it was huge and my daughter got Spaghetti and Meatballs and it was very, very, good. I tried it and it was homemade and delicious. They also had fancy drinks for kids, parrot mask, and a cool interior - boat booths, ect. and the volcano!!
I think older kids would like the Hard Rock just because it is "cool". I'm not sure how old your kids are - so that may sway your decision.
Have fun deciding!!