Generally speaking the larger the trampoline the higher the bounce. This is because larger trampolines usually have more springs and larger springs. Larger trampolines therefore need to support a greater force which is why they are stronger, heavier and have thicker tubing for the frame.
8 ft trampolines and 14 ft trampolines do not differ significantly in terms of safety. However larger trampolines tend to be higher from the ground and produce higher bounces which means the user has higher to fall should they be propelled onto the ground.
Larger trampolines will tend to be more expensive then smaller ones. Here are the most common sizes:
8ft Trampolines. These are popular and accommodate most peoples needs. These are a perfect cheaper trampoline option for single use by children.
10ft Trampolines. Also very popular they tend to have a slightly higher bounce then the 8ft trampolines and are great for slightly older children.
12ft Trampolines are a good sized round trampoline yet are still small enough for most gardens. They can also be used by two bouncers at once including teenages and adults.
14ft Trampolines are some of the largest commercially available trampolines within a reasonable price. They offer stability and control for up to 3 bouncers at once.