For a Volkswagen Golf Mk7, a rear spoiler that is worth buying would depend on your personal preferences, the type of driving you do, and the style of the car. Here are a few options:

OEM Spoiler: An OEM spoiler is a factory-style spoiler that is designed specifically for your Golf Mk7. It is a safe choice if you want to maintain the original look of your car. The VW Performance Spoiler is a popular OEM option for the Golf Mk7.

TCR Style Spoiler: A TCR style lip spoiler is a subtle modification that provides a sporty look without being too flashy. It mounts to the top edge of the trunk and extends slightly beyond it.

Oettinger Style Spoiler: A oettinger style wing spoiler provides a more aggressive look and better aerodynamics. It mounts to the trunk and extends high above the roofline.

Injection Mold Type Spoiler: A injection mold type roof spoiler mounts to the top edge of the rear window and extends outwards. It provides a unique look and can improve aerodynamics.

Ultimately, the style of rear spoiler worth buying for a Golf Mk7 will depend on your personal preferences and the type of driving you do. It's always a good idea to do research and read reviews before making a purchase.