Be careful with your choices, there are racks that are much less good quality and can cause problems on your vehicle and even bicycles. If I may pick a few brands I would suggest a comparison such as: Hollywood Racks, Topeak, Thule, Saris,
Men’s Short Sleeve Polo Shirts, Bike Racks Allen, Racor,
Ralph Lauren Womens Shorts, Bell, Swagman,
Ralph Lauren US Polo, Wald as your reference in determining the choice of the best. What are the advantages for you when using 4 bike racks; you can carry more than one bike.