What is the difference between the different types of trampoline?
Some are bouncier than others. It depends on a few things;
The size of the bed/frame;
The bigger the frame the better; not only is is it slightly more bouncy, but the bigger the trampoline is, the more comfortable it is to bounce on.
The bed; The narrower the bands that make up the bed, the bouncier the trampoline is. This is mainly to do with air resistance, and a little to do with stretch. A trampoline with a mesh bed that has no holes will not be very bouncy at all. Common sizes are 3/4", 1/2", 6mm, 6x4mm. This defines the width of each band that makes up the bed.
The shape?
Not especialy for technical reasons, but the round garden trampolines tend to be far less bouncy than the rectangular trampolines. The reason for this is mainly because of the points above