Well a suspension fork isn't going to help you with sand. In my opinion, any of the bikes mentioned here would be great. Once you get north of 500$ from a reputable brand it's hard to buy a bad bike.

Just to be clear, when it comes to riding through dirt, or sand, or gravel, all the suspension fork is going to do is make the ride more comfortable. It's not going to make it any easier to push the bike through that terrain. You can ride a hybrid bike with a rigid fork through gravel and dirt if the tires are the right size, you'll just be a lot bumpier doing it. So wether or not you think you should go with a rigid fork or a suspension fork depends entirely on how much time you plan to spend in those conditions.