If you can swing the points (and the miles), I would strongly recommend the St Regis Princeville. Great Plat recognition, outstanding staff and breathtakingly beautiful surroundings. I dont know what the crowds will be like in May but the island of Kauai is serene and offers spectacular hikes and other outdoor activities. The hotel beach is not the greatest but there are plenty of good beaches nearby and the pool is quite nice. You can split your stay across the Westin (Cat 5) and the St Regis (Cat 6) if you are short on points although I think the St Regis is probably worth splurging for.