Of the three hotels you are considering, the Sheraton property is closest the the Queen's Beach area, the one with the best channel for good swimming.
Swimming is safe in very Waikiki, but we have the occasional visitor drowning. It isn't the nature of the beach or water, but I suspect it is due to people with underlying medical conditions who have had their bodies physically stressed by the travel. If you are fit (and don't ignore the signs warning your not to dive off the groin into shallow water) you will be fine.
Another good place to swim is at Ala Moana Beach park. You might check out hotels in that are closer to that area, such as the Ala Moana Hotel or the Alana Doubletree.
Enjoy your first trip to Hawaii!