Best vacuum for hardwood

What is the best vacuum that won't scratch the hardwood floor ? We just moved to a new house that doesn't have a central vacuum so we are not sure which one to buy. The 2 floors are hardwood with hardwood stairs. We want to make sure they don't get scratch. We will probably buy it during Black Friday. Budget would be about $500 or so but we are open. I just want to make sure it works good and my hardwood will stay good. We have 2 very messy toddlers and we are all loosing lots of hair !!!